#include <stdio.h>
#define TAKA 1
#define AOKI 0

int main(void){
    int a,b,c,d,turn=TAKA;
    scanf("%d %d %d %d",&a,&b,&c,&d);

    while(a>0 && c>0){
        if(turn == TAKA){
            c -= b;
            turn = AOKI;
        }else{
            a -= d;
            turn = TAKA;
        }
    }

    if(a<=0){
        printf("No\n");
    }else{
        printf("Yes\n");
    }

    return 0;
}