#include <iostream>
#include <cmath>

using namespace std;

int power(short a, short b) {
    int result = 1;

    while (b > 0) {
        b--;

        result *= a;
        result %= 1000000007;
    }

    return result;
}

int main() {
    short a, b, k, c;
    int result;

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

    if (c != a && c != b) {
        result = 0;
    } else if (a == b) {
        result = k;
    } else {
        result = (power(2, k - 1) * k) % 1000000007;
    }

    cout << result << endl;

    return 0;
}