// compile: make data
// run: ./data < data.in
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#include <debug/codeforces.h>
#define debug(x...) _debug_print(#x, x);
#define Debug(x...) _debug_print_format(#x, x);
std::ifstream terminal("/dev/tty");
#define PP cerr<<"\033[1;30mpause...\e[0m",terminal.ignore();
#else
#define debug(x...)
#define Debug(x...)
#define PP
#endif
template<typename...Args> void print_(Args...args){((cout<<args<<" "),...)<<endl;}
#define rep(i,a,b) for(int i=(a);i<(int)(b);++i)
#define sz(v) ((int)(v).size())
#define print(...) print_(__VA_ARGS__);
#define FIND(a, x) ((find(a.begin(),a.end(),(x))!=a.end())?1:0)
#define cmin(x,...) x=min({(x),__VA_ARGS__})
#define cmax(x,...) x=max({(x),__VA_ARGS__})
#define INTMAX (int)(9223372036854775807)
#define INF (int)(1152921504606846976)
#define NaN (int)(0x8b88e1d0595d51d1)
#define double long double
#define int long long
#define uint unsigned long long
#define MAXN 200010

struct graph {
    struct node {
        int u, v, w;
        int idx;
        int used = 0;
        bool operator<(const node &other) const {return w < other.w; }
        bool operator==(const node &other) const {return v == other.v && w == other.w; }
    };
    vector<vector<node>> e;
    vector<vector<int>> invid;
    node &inv(node &edge) {return e[edge.v][invid[edge.u][edge.idx]]; }

    int n;
    bool directed;
    graph(int V, bool D = 0) {
        n = V;
        e.resize(n), invid.resize(n);
        directed = D;
    }
    void add_edge(int u, int v, int w = 1, int wb = 1) {
        e[u].push_back(node{u, v, w, sz(e[u])});
        if (!directed) {
            e[v].push_back(node{v, u, wb, sz(e[v])});
            invid[u].push_back(sz(e[v]) - 1);
            invid[v].push_back(sz(e[u]) - 1);
        }
    }
    vector<vector<int>> cc() {
        vector<vector<int>> res;
        vector<bool> vis(n, 0);
        function<void(int)> dfs = [&](int u) {
            vis[u] = 1;
            res.back().push_back(u);
            for (auto &edge: e[u]) if (!vis[edge.v]) dfs(edge.v);
        };
        rep(i, 0, n) {
            if (!vis[i]) res.push_back(vector<int>()), dfs(i);
        }
        return res;
    }
    vector<pair<int, int>> bridge() {
        vector<int> dfn(n), low(n), parent(n, -1);
        vector<pair<int, int>> res;
        int clock = 0;
        function<void(int, int)> dfs = [&](int u, int p) {
            parent[u] = p;
            low[u] = dfn[u] = ++clock;
            for (auto &edge: e[u]) {
                if (!dfn[edge.v]) {
                    dfs(edge.v, u);
                    cmin(low[u], low[edge.v]);
                    if (low[edge.v] > dfn[u]) res.push_back({parent[edge.v], edge.v});
                }
                else if (dfn[edge.v] < dfn[u] && edge.v != p) cmin(low[u], dfn[edge.v]);
            }
        };
        rep(i, 0, n) if (!~parent[i]) dfs(i, i);
        return res;
    }
    void graphviz_dump(int plus = 0, string filename = "graph.dot") {
        ofstream gf; gf.open(filename);
        gf << (directed ? "digraph" : "graph") << " {\n";
        gf << "    "; rep(i, 0, n) gf << i+plus << " ;"[i==n-1]; gf << endl;
        string notation = directed ? " -> " : " -- ";
        bool weighted = 0;
        for (auto es: e) for (auto edge: es) if (edge.w != 1) weighted = 1;
        rep(u, 0, n) {
            for (auto edge: e[u]) {
                int v = edge.v, w = edge.w;
                if (!directed && u > v) continue;
                gf << "    " << u+plus << notation << v+plus << (weighted ? " ;\n" : ";\n");
            }
        }
        gf << "}\n";
    }
    void search() {
        function<void(int)> dfs = [&](int u) {
            for (auto &edge: e[u]) {
                if (edge.used || inv(edge).used) continue;
                edge.used = 1;
                dfs(edge.v);
            }
        };
        dfs(0);
    }
};

int32_t main() {
    ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

    int n, m; cin >> n >> m;
    graph g(n);
    rep(i, 0, m) {
        int u, v; cin >> u >> v; --u, --v;
        g.add_edge(u, v);
    }
    auto cc = g.cc();
    auto bridge = g.bridge();
    if (sz(cc) > 1 || !bridge.empty()) {
        cout << "IMPOSSIBLE" << endl;
        return 0;
    }
    g.search();
    rep(i, 0, sz(g.e)) {
        for (auto &edge: g.e[i]) {
            if (edge.used) cout << i+1 << " " << edge.v+1 << endl;
        }
    }

    return 0;
}