#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<ll> vll;
typedef vector<vll> vvll;
#define REP(i, n) for(ll i = 0; i < n; ++i)
#define REPs(i, x, n) for(ll i = x; i < n; ++i)
#define endli "\n"

ll power(ll a, ll b){
    ll temp = a;
    REPs(i, 1, b){
        a = a * temp;
        a %= 1000000007;
    }
    return a;
}

int main(){
    ll a, b, k,c;
    cin >> a >> b >> k >> c;
    ll hell;
    ll vystup = 1;
    if(a != b){
        hell = power(2, k)*k;
        hell%=1000000007;
        if(c == a || c == b){
            vystup = hell/2;
        }
        else {
            vystup = 0;
        }
    } else {
        hell = 1;
        vystup = k;
        if(c != a){
            vystup = 0;
        }
    }
    cout << vystup << endli;
    return 0;
}