#include <stdio.h>

int main() {
    int A, B, C, D;
    
    scanf("%d %d %d %d", &A, &B, &C, &D);

    while((A > 0) || (C > 0)) {
        C -= B;
        A -= D;
    }

    if((A <= 0) && (C <= 0)) {
        printf("Yes");    
    } else if(A <= 0) {
        printf("No");
    } else if(C <= 0) {
        printf("Yes");
    }

    return 0;
}