#include <iostream>

int main(){
    int a, b, c, d;
    std::cin >> a >> b >> c >> d;
    while(1){
        c -= b;
        if(c <= 0){
            std::cout << "Yes" << std::endl;
            break;
        }
        a -= d;
        if(a <= 0){
            std::cout << "No" << std::endl;
            break;
        }
    }
}
