Substitute C++

#include <iostream>
using namespace std;
int main()
{
    int K, L, M, N;
    cin >> K >> L >> M >> N;

    if (K % 2 == 1)
        K++;

    if (M % 2 == 1)
        M++;

    if (L % 2 == 0)
        L++;

    if (N % 2 == 0)
        N++;

    int substitutes = 0;

    for (int k = K; k <= 8 && substitutes < 6; k += 2)      // [K,8]
    {
        for (int l = 9; l >= L && substitutes < 6; l -= 2)      // [9,L]
        {
            for (int m = M; m <= 8 && substitutes < 6; m += 2)      // [M,8]
            {
                for (int n = 9; n >= N && substitutes < 6; n -= 2)      // [9,N]
                {
                    if (k == m && l == n)
                        cout << "Cannot change the same player.\n";
                    else
                    {
                        cout << k << l << " - " << m << n << endl;
                        substitutes++;
                    }
                }
            }
        }
    }

    return 0;
}