#include <stdio.h>
#include <string.h>
int main(void)
{
    int  a,b[200000],i,j,n=0,m,x,y,z=0;
    char c[10100],s[10100];

    scanf("%d%d%d%d",&n,&x,&m,&y);//n,m hp  x,y at

    while(1){
        m=m-x;
        if(m<=0){printf("Yes"); break;}
        n=n-y;
        if(n<=0){printf("No"); break;}
    }
    
    printf("\n");
    return 0;
}