#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
const long long MOD = 1000000007;
long long P, Q, N, K;
long long p[101], q[101], d[101];
long long inv(long long tar) {
long long ret = 1;
for(int i = 30; i >= 0; i--) {
ret = ret * ret % MOD;
if((1ll << i) & (MOD - 2)) ret = ret * tar % MOD;
}
return ret;
}
int main(void) {
cin >> P >> Q >> N >> K;
if(K == 0) printf("0\n");
else if(K == N) printf("1\n");
else {
long long gcdv = __gcd(Q, P);
long long a = Q / gcdv * inv(P / gcdv) % MOD;
gcdv = __gcd(P - Q, P);
long long b = (P - Q) / gcdv * inv(P / gcdv) % MOD;
p[N - 1] = a, q[N - 1] = b;
for(int i = N - 2; i > 0; i--) {
long long base = ((1 - b * p[i + 1] % MOD) + MOD) % MOD;
p[i] = a * inv(base) % MOD;
q[i] = b * q[i + 1] % MOD * inv(base) % MOD;
}
d[0] = 0;
for(int i = 1; i < N; i++) d[i] = (d[i - 1] * p[i] % MOD + q[i]) % MOD;
cout << d[K];
}
return 0;
}
