#include <stdio.h>

int main(void)
{
    long H, W, N, K;
    scanf("%ld%ld%ld%ld", &H, &W, &N, &K);
    if (((H - 1) + (W - 1)) % N + 1 == K) puts("YES");
    else puts("NO");
    return 0;
}