#include <iostream>
#include <algorithm>

using namespace std;

int comb(int h, int t) {
    int cislitel = h;
    int l = t;
    int p = h - t;

    if (h == t || t == 0) {
        return 1;
    }

    if (l > p) swap(l, p);

    for (int i = cislitel - 1; i > p; i --) {
        cislitel *= i;
    }

    for (int i = l; i > 0; i--) {
        cislitel /= i;
    }

    return cislitel;
}

int main() {
    int a;
    int b;
    int k;
    int c;
    scanf("%d %d %d %d", &a, &b, &k, &c);

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

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

    int result = 0;

    for (int i = k; i > 0; i--) {
        result += i * comb(k, i);
    }

    cout << (result % 1000000007) << endl;
    return 0;
}