#include <bits/stdc++.h>

using namespace std;

using i64 = long long;

void solve(){
    int n;
    cin >> n;
    vector<int>a(n);
    for (int i = 0;i < n;i ++){
        cin >> a[i];
    }
    for (int i = 0;i < n - 1;i ++){
        if (a[i] <= 0){
            cout << "No\n";
            return;
        }
    }
    cout << "Yes\n";
}       

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

    int T = 1;
    // cin >> T;
    while (T--) {
        solve();    
    }
    return 0;
}