#include <stdio.h>

int main(){

    int A;
    int B;
    int C;
    int D;
    scanf("%d",&A);
    scanf("%d",&B);
    scanf("%d",&C);
    scanf("%d",&D);

    
    while(A>0 || C>0){
        A = A-D;
        C = C-B;
    }

    if(A>0){
        printf("Yes");
    }else
    printf("No");


    return 0;

}