#include <iostream>

using namespace std;


int main() {
    int a,b,k,c;
    long long int sum = 0;
    long long nasobic;
    long long mod = 1000000007;

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

    if ( (c != a) && (c != b) )
    {
        cout << 0 << endl;
        return 0;

    }
    nasobic = k;
    if(a == b)
    {
        cout << k;
        return 0;
    }

    for(int i = k - 1; i > 1; i-- )
    {
        nasobic *= i;
        nasobic = nasobic % mod;
        if (nasobic == 0)
            break;
        sum = sum % mod;
        sum += nasobic;
    }

    sum += 2* k;
    cout << sum << endl;
    return 0;
}