#include <cstdio>
using namespace std;
const long long MOD = 1000000007ll;
int m;
int face[10000];
long modpow(long long r, long long n) {
long long ret = 1;
while (n > 0) {
if (n % 2 > 0) {
ret = (ret * r) % MOD;
}
r = (r * r) % MOD;
n /= 2;
}
return ret;
}
long long modinv(int n) {
return modpow(n, MOD - 2);
}
long long gcd(int a, int b) {
if (a < b) {
return gcd(b, a);
}
return (b == 0) ? a : gcd(b, a % b);
}
long long num[200], denom[200];
long long coff[200];
void proc() {
int p, q, n, k;
scanf("%d %d %d %d", &p, &q, &n, &k);
if (k == n) {
printf("1");
return;
}
if (k == 0) {
printf("0");
return;
}
long long g;
coff[1] = ((p - q) * modinv(p)) % MOD;
num[1] = p - q; denom[1] = p;
g = gcd(num[1], denom[1]);
num[1] /= g; denom[1] /= g;
for (int i = 2; i < n; ++i) {
long long t = ((p - q) * modinv(p)) % MOD;
long long u = (((coff[i - 1] * q) % MOD) * modinv(p)) % MOD;
long long v = (1 - u + MOD) % MOD;
coff[i] = (t * modinv(v)) % MOD;
}
long long res = 1;
for (int i = n - 1; i >= k; --i) {
res = (res * coff[i]) % MOD;
}
printf("%lld", res);
}
int main() {
//freopen("input.txt", "r", stdin);
proc();
return 0;
}
