#include<stdio.h>

int main(void)
{
    int a,b,c,d,z,g;

    scanf("%d%d%d%d",&a,&b,&c,&d);
    z=1;
    while(1){
        c-=b;
        if (c<=0) {printf("Yes\n"); break;}
        a-=d;
        if (a<=0) {printf("No\n"); break;}
    }
    return 0;
}