#include typedef long long ll; using namespace std; int INF = 1LL << 30; int MOD = 1e9+7; main(){ ll H,W,N,K; cin >> H >> W >> N >> K; if(N == 1 || (H + W - 1) % N == K % N){ cout << "YES" << endl; } else{ cout << "NO" << endl; } }