#include<bits/stdc++.h>
using namespace std;

typedef long long ll;

const ll MOD = 1e9 + 7;

long long a, b, c, k;

ll qpow (ll a, ll b) {
	ll s = 1;
	while (b) {
		if (b & 1) s = s * a % MOD;
		a = a * a % MOD;
		b /= 2;
	}	
	return s;
}

int main(){
	cin >> a >> b >> k >> c;
	
	if (a == c || c == b) cout << k * qpow (2, k - 1) % MOD;
	else cout << 0 << endl;
}