#include <iostream>
#define MOD 1000000007


using namespace std;



int main(){
    int a,b,c,k;
    cin >> a >> b >> k >> c;
    if (c != a && c != b) {
        cout << 0 << endl;
        return 0;
    }
    if (a == b) {
        cout << k << endl;
        return 0;
    }
    long long r = 1;
    for (int i=0; i<k-1; i++){
        r *= 2;
        r %= MOD;
    }
    cout << (r * k) % MOD << endl;
}