#include <stdio.h>
int main(void){
    int a, b, c, d;
    
    scanf("%d %d %d %d", &a, &b, &c, &d);
    
    for(;;){
        c = c - b;
        if(c < 1){
            printf("Yes\n");
            break;
        }
        a = a - d;
        if(a < 1){
            printf("No\n");
            break;
        }
    }
    
}
