#include <bits/stdtr1c++.h>

using namespace std;

typedef double ld;
ld a[2][505][505], a_[2][505][505], b[2][505];
int main() {
    ios::sync_with_stdio(0);
    int n; cin >> n;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            cin >> a[0][j][i];
            a_[0][i][j] = a[0][j][i];
        }
    }

    for (int iter = 1; iter < (n < 300 ? 19 : 7); iter++) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                a[iter&1][i][j] = 0;
                for (int k = 0; k < n; k++) {
                    a[iter&1][i][j] += a[(iter&1)^1][i][k] * a_[(iter&1)^1][j][k];
                }
                a_[iter&1][j][i] = a[iter&1][i][j];
            }
        }
    }

    for (int i = 0; i < n; i++) {
        b[0][i] = a[0][i][0];
    }

    int iter = 1, max_iters = 100;
    while (max_iters--) {
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < n; j++) {
                b[iter][i] += a[0][i][j] * b[iter^1][j];
            }
        }
        iter ^= 1;
    }

    ld sum = 0;
    for (int i = 0; i < n; i++) {
        sum += b[0][i];
    }
    cout << fixed << setprecision(8) << b[0][0]/sum << endl;
    return 0;
}