w

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n, cnt=0;
    cin >> n;
    vector <int> a(n);
    for (int i = 0; i<n; i++) {
        cin >> a[i];
    }
    for (int i = 1; i<n; i++) {
        if (a[i-1]<0 and a[i]<0 or a[i-1]>=0 and a[i]>=0) {
            cout << "YES";
            cnt++;
            break;
        }
    } if (cnt==0) {
        cout << "NO";
    }
}