// compile: g++ -o data data.cpp -std=gnu++20 -DLOCAL
// run: ./data < data.in
#include <bits/stdc++.h>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#endif
#define sz(v) ((int)(v).size())
#define PV(v) for (int i=0;i<v.size();++i)cout<<v[i]<<" ";cout<<endl;
#define INTINF 9223372036854775807
#define int long long

using namespace std;

int32_t main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    int n; cin >> n;
    vector<int> h(n+1, 0);
    for (int i = 0; i < n-1; ++i) {
        int x; cin >> x;
        ++h[x];
    }
    for (int i = 1; i <= n; ++i) {
        if (!h[i]) {
            cout << i << endl;
            break;
        }
    }

    return 0;
}