#include using namespace std; #define REP(i,n) for(int i=0;i ostream& operator<<(ostream& os,const vector& vec){ os << "["; for(const auto& v : vec){ os << v << ","; } os << "]"; return os; } const long long mod = 1e9+7; typedef long long ll; typedef unsigned long long ull; typedef pair pii; typedef vector vi; typedef vector vvi; typedef vector vll; typedef vector vvll; int main(){ ll H,W,N,K;cin>>H>>W>>N>>K; K--; ll t = H+W-1; if(t==1){ if(K==0) cout << "YES" << endl; else cout << "NO" << endl; return 0; } if(t%N==K) cout << "YES" << endl; else cout << "NO" << endl; }