#include <stdio.h>

int main(int argc, char **argv) {
    int a, b, c, d ;
    scanf("%d %d %d %d", &a, &b, &c, &d) ;

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