#include <iostream>

using namespace std;

int factorial( int n )
{
    int res = 1;

    for( int i = 1; i <= n; i++ )
    {
        res *= i;
    }

    return res;
}

int comb_number(int num, int n_fact, int k )
{
    int result = 0;

    result = n_fact / (factorial(k ) * factorial(num - k ));

    return result * k;
}

int main( )
{
    int a, b, k ,c;
    int k_fact;
    int res = 0;
    cin >> a >> b >> k >> c;

    k_fact = factorial( k );

    for( int i = 1; i <= k; i++ )
    {
        res += comb_number( k, k_fact, i );
    }

    cout << res << endl;

    return 0;
}