#include<stdio.h>

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

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

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