#include <stdio.h>

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

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

    while (A > 0) {
        C = C - B;
        if (C <= 0) {
            break;
        }
        A = A - D;
    }

    if (C <= 0) {
        printf ("Yes\n");
    } else {
        printf ("No\n");
    }

    return 0;
}