#include <stdio.h>
int main(void)
{
    int A,B,C,D,E,F;
    scanf("%d %d %d %d",&A,&B,&C,&D);
    if(C%B == 0){
        E = C/B;
    }else{
        E = C/B+1;
    }
    if(A%D == 0){
        F = A/D;
    }else{
        F = A/D+1;
    }
    if(E <= F){
        printf("Yes");
    }else{
        printf("No");
    }
}