#include <iostream>
#include <cstdlib>
#include <cmath>

using namespace std;

int main() {
    int a, b, c, k;
    long long int result = 0;

    cin >> a >> b >> k >> c;

    result += k * 2;

    long long int tmp_result;

    for (int i = 2; i < k; i++) {

        tmp_result = 1;

        for ( int braces = 0 ; braces < i ; braces++ )
            tmp_result *= k - braces;

        tmp_result = ( tmp_result / 2 ) * i;
        result += tmp_result;
        //cout << tmp_result << ", " << result << endl;
    }

    cout << result % 1000000007 << endl;


    return 0;
}