#include<stdio.h>

int main(){
    int a,b,c,d;
    scanf("%d %d %d %d ",&a, &b, &c, &d );

    while(1){
        c = c - a;
        if(c <= 0){
            printf("Yes\n");
            break;
        }
        b = b - d;
        if(c <= 0){
            printf("No\n");
            break;
        }

    }
    return 0;
}