#include<stdio.h>

int main(void){
    int A, B, C, D;
    scanf("%d%d%d%d", &A, &B, &C, &D);

    for (int i = 0; i < 100; i++) {
        C = C - B;
        if (C <= 0) {
            printf("Yes\n");
            break;
        }
        A = A - D;
        if (A <= 0) {
            printf("No\n");
            break;
        }
    }
    return 0;
}
