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

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

    scanf("%ld %ld %ld %ld", &a, &b, &k, &c);

    if (c==a || c==b)
        printf("%d", (int)k*(int)pow(2, k-1)%1000000007);
    else
        printf("%d", 0);


    return 0;
}