#include <stdio.h>

int main(void){

    int  a, b, c, d;

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

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

    }
    return 0;
}