#include <stdio.h>

int main(void){

    int A = 0;
    int B = 0;
    int C = 0;
    int D = 0;

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

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

    if (C<= 0){
        printf("Yes\n");
    } else {
        printf("No\n");
    }
    
    return 0;
}