#include<stdio.h>
#define ll long long 
int main(){
    int a, b, c, d;
    scanf("%d%d%d%d",&a,&b,&c,&d);
    int p = (a + d - 1) / d;
    int q = (c + b - 1) / b;
    if(p >= q)
        puts("Yes");
    else
        puts("No");
    return 0;
}