#include <bits/stdc++.h>
#define ll long long int
using namespace std;

const int mod=1e9+7;

ll p(ll a,ll b)
{
    if(b==0) return 1LL;
    ll res=p(a,b/2);
    res%=mod;
    res*=res;
    res%=mod;
    if(b%2==1) res*=a;
    res%=mod;
    return res;
}

int main()
{
ll a,b,k,c; cin>>a>>b>>k>>c;
long long int res=0;
    if(c!=a && c!=b)
    {
        cout<<0<<endl; return 0;
    }
    else if(c==a && c==b)
    {
        cout<<k<<endl;
        return 0;
    }
    else
    {
        res=p(2,k-1);
        res%=mod;
        res*=(ll)(k);
        res%=mod;
        cout<<res<<endl;
    }
    return 0;
}