
#include <stdio.h>

int main(void) {
    int A, B, C, D;
    scanf("%d", &A);
    scanf("%d", &B);
    scanf("%d", &C);
    scanf("%d", &D);
    int a, c;
    a = A / D;
    c = C / B;
    
    if (B>=C){
        printf("Yes");
    }else if (D>=A){
        printf("No");
    }else if (a<=c){
        printf("Yes");
    }else if (a>c){
        printf("No");
    }
}