#include <math.h>
#include <stdio.h>
#include <string.h>
int a, b, c, d;
int main(void) {
    scanf("%d %d %d %d", &a, &b, &c, &d);
    do {
        c = c - b;
        if (c < 1) {
            printf("Yes\n");
            break;
        }
        a = a - d;
        if (a < 1) {
            printf("No\n");
            break;
        }
        

    } while (1);
}