#include <stdio.h>

int main(int argc, char const *argv[])
{
    int a, b, c, d;
    int turn;

    scanf("%d %d %d %d", &a, &b, &c, &d);
    turn = 1;
    while(1) {
        if(turn) {
            c -= b;
            turn = 0;
        } else {
            a -= d;
            turn = 1;
        }
        if(a <= 0) {
            printf("No\n");
            return 0;
        } else if(c <= 0) {
            printf("Yes\n");
            return 0;
        }
    }
}