Histogram

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;
    int h[n + 1];
    for (int i = 1; i <= n; ++i) {
        cin >> h[i];
    }

    stack<int> st;
    int L[n + 1], R[n + 1];

    for (int i = 1; i <= n; ++i) {
        while (!st.empty() && h[st.top()] >= h[i]) {
            st.pop();
        }

        if (st.empty()) {
            L[i] = 1;
        } else {
            L[i] = st.top() + 1;
        }

        st.push(i);
    }

    while (!st.empty()) {
        st.pop();
    }

    for (int i = n; i >= 1; --i) {
        while (!st.empty() && h[st.top()] >= h[i]) {
            st.pop();
        }

        if (st.empty()) {
            R[i] = n;
        } else {
            R[i] = st.top() - 1;
        }

        st.push(i);
    }

    long long ans = 0;

    for (int i = 1; i <= n; ++i) {
        ans = max(ans, h[i] * (R[i] - L[i] + 1ll));
    }

    cout << ans;
    return 0;
}

/*
10
i       1 2  3 4 5 6 7 8 9  10
h       2 1  3 4 5 4 7 3 1  7
L       1 1  3 4 5 4 7 3 1  10
R       1 10 8 7 5 7 7 8 10 10

long long ans = 0;

for (int i = 1; i <= n; ++i) {
    ans = max(ans, h[i] * (R[i] - L[i] + 1));
}

i       1 2  3 4 5 6 7 8 9  10
h       2 1  3 4 5 4 7 3 1  7
L       1 1  3 4 5 4 7 3 1  10
R       1 10 8 7 5 7 7 8 10 10

st = {2}
*/