def reverseMovement(matrA, matrB, M):
    for i in reversed(range(M)):
        for j in reversed(range(0, i)):
                l = matrA[j][i]/matrA[i][i]
                matrA[j][i] -= (l * matrA[i][i])
                for k in range(M):
                    matrB[j][k] -= (l * matrB[i][k])