#include <iostream>
#include <stdio.h>
#include <math.h>

int factorial(int k, int i);

using namespace std;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);

    int a, b, k, c;

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

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

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

    int result = 0;
    for (int i = 0; i <= k; i++) {
        result += i * factorial(k, i);
        if (result >= 1000000007) {
            result = result % 1000000007;
        }
    }
    cout << result << endl;

    return 0;
}

int factorial(int k, int i) {
    int result = 1;
    if (i < k - i) i = k - i;
    for (int j = k; j > i; j--) {
        result *= j;
    }
    for (int j = k - i; j > 0; j--) {
        result /= j;
    }
    return result;
}