#include<bits/stdc++.h>

#define REP(i,s,n) for(int i=s;i<n;i++)
#define rep(i,n) REP(i,0,n)

using namespace std;

typedef long long ll;

int main(){
  ll h,w,n,k;
  cin >> h >> w >> n >> k;
  ll loser = h * w;
  loser %= n;
  loser = ( loser - 1 + n ) % n;
  --k;
  puts((loser==k)?"YES":"NO");
  return 0;
}