#include <bits/stdc++.h>

using namespace std;

typedef long long LL;

const LL MOD = 1e9 + 7;

LL fastpow(LL a, LL exp)
{
    LL res = 1;

    while(exp)
    {
        if(exp & 1)
        {
            res = (res * a) % MOD;
        }

        a = (a * a) % MOD;
        exp >>= 1;
    }

    return res;
}

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

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

    if(k == 0 || (c != a && c != b))
    {
        cout << 0;
        return 0;
    }
    
    if(a == b)
    {
        cout << k;
        return 0;
    }
    
    cout << (k * fastpow(2, k - 1)) % MOD;

    return 0;
}