#include <stdio.h>

int main (void)
{
    int A,B,C,D;

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


    while(1){
        C = C - B;
        A = A - D;
        if(C <= 0){
            printf("Yes\n");
            break;
        }
        else if(A <= 0){
            printf("No\n");
            break;
        }
        
    }
    return 0;

}
