#include <stdio.h>
int main(void){

    int A, B, C, D;
    int tATK,aATK;

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

    aATK = (A-1) / D;
    tATK = (C-1) / B;

    if(aATK>=tATK){
        printf("Yes");
    }else{
        printf("No");
    }
    return 0;
}