Z-4

#include <iostream>
#include <string>
#include <fstream>
#include <queue>

using namespace std;

const int N = 1111;
int n;
double a[N][N];

bool calc() {
    bool ok = 0;
    for (int k = 0; k < n; ++k)
        for (int i = 0; i < n; ++i)
            for (int j = 0; j < n; ++j)
                if (a[i][k] * a[k][j] > a[i][j]) {
                    ok = 1;
                    a[i][j] = a[i][k] * a[k][j];
                }
    for (int i = 0; i < n && ok; ++i)
        if (a[i][i] > 1) ok = 0;
    return ok;
}

int main(){
    ifstream fin("in.txt");
    ofstream fout("out.txt");
    fin >> n;
    for (int i = 0; i < n; ++i)
        for (int j = 0; j < n; ++j)
            fin >> a[i][j];
    while (calc());
    for (int i = 0; i < n; ++i)
        if (a[i][i] > 1) {
            fout << "yes";
            return 0;
        }
    fout << "no";
    return 0;
}