// compile: g++ data.cpp /usr/include/c++/12/debug/cpglib/print.o -o data -O1 -std=gnu++20 -Wall -Wextra -Wshadow -D_GLIBCXX_ASSERTIONS -fmax-errors=2 -DLOCAL
// run: time ./data < data.in
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#include <debug/cpglib/print.h>
#define debug(x...) _debug_print(0, #x, x);
#define Debug(x...) _debug_print(1, #x, x);
#define DEBUG(x...) _debug_print(2, #x, x);
std::ifstream terminal("/dev/tty");
#define PP cerr<<"![1;30mpause...\e[0m",terminal.ignore();
#else
#define debug(x...)
#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 endl "\n"
#define MAXN 200010
 
int32_t main() {
    ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
 
    int n, m; cin >> n >> m;
    vector<vector<bool>> a(n, vector<bool>(m, 0));
    vector<queue<int>> col(m);
    rep(i, 0, n) {
        string s; cin >> s;
        rep(j, 0, m) {
            a[i][j] = s[j] == '*';
            if (a[i][j]) col[j].push(i);
        }
    }
    rep(j, 0, m) col[j].push(n);
    int ans = 0;
    rep(i, 0, n) {
        // first: start col, second: height
        stack<pair<int, int>> st;
        rep(j, 0, m) if (col[j].size() && col[j].front() < i) col[j].pop();
        rep(j, 0, m) {
            int sc = j; // start col
            while (st.size() && st.top().second > col[j].front() - i) {
                auto [c, h] = st.top(); st.pop();
                cmax(ans, (j - c) * h);
                sc = c;
            }
            st.push({sc, col[j].front() - i});
        }
        while (st.size()) {
            auto [c, h] = st.top(); st.pop();
            cmax(ans, (m - c) * h);
        }
    }
    cout << ans << endl;
 
    return 0;
}