#include<stdio.h>

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

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

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

    return 0;
}
