#include <iostream>
#include <cmath>
#include <vector>

using namespace std;
const int n = 4;
vector<vector<double>> a(n, vector<double>(n, 0));
vector<double> b(n, 0), x(n, 0);

void reverse(int k, int r)
{
    double c;
    for (int j = k; j < n; j++)
    {
        c = a[k][j];
        a[k][j] = a[r][j];
        a[r][j] = c;
    }
    c = b[k];
    b[k] = b[r];
    b[r] = c;
}
void dv(int k)
{
    for (int j = k + 1; j < n; j++)
        a[k][j] /= a[k][k];
    b[k] /= a[k][k];
}

void clear(int k, int r)
{
    for (int j = k + 1; j < n; j++)
        a[r][j] -=  a[k][j] * a[r][k];
    b[r] -= b[k] * a[r][k];
}

int main()
{
    setlocale(LC_ALL, "Russian");
    cout << "Введите коэфиценты" << endl;
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            cin >> a[i][j];
    cout << "Введите свободные члены" << endl;
    for (int i = 0; i < n; i++)
        cin >> b[i];
    for (int k = 0; k < n - 1; k++)
    {
        if (a[k][k] == 0)
        {
            int i = k + 1;
            while (a[i][k] == 0)
                i++;
            reverse(k, i);
        }
        dv(k);
        for (int i = k; i < n; i++)
            clear(k, i);
    }
    dv(n - 1);
    for (int i = n-1; i >= 0; i--)
    {
        x[i] = b[i];
        for (int j = i + 1; j < n; j++)
            x[i] -= a[i][j] * x[j];
        cout << "x[" << i << "]=" << x[i] << endl;
    }
}