#include <stdio.h>

int main(void)
{
    int A,B,C,D;

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

    while(1){
        C = C - B;
        if(C <= 0){
            printf("Yes\n");
            return 0;
        }
        A = A - D;
        if(A <= 0){
            printf("No\n");
            return 0;
        }

    }

}