#include<bits/stdc++.h>

using namespace std;

struct INIT{
    INIT(){
	ios::sync_with_stdio(false);
	cin.tie(0);
    }
}init;

int main(){
    long long R,C,N,K;
    cin>>R>>C>>N>>K;
    if(R==1||C==1)
	cout<<(((R*C+N-1)%N+1==K)?"YES":"NO")<<endl;
    else
	cout<<((((R-1)*(C-1))%N+1==K)?"YES":"NO")<<endl;
    return 0;
}