#include <iostream> #include <string> #include <vector> #include <algorithm> #include <functional> #include <cmath> #include <iomanip> #include <stack> #include <queue> #include <numeric> #include <map> #include <unordered_map> #include <set> #include <fstream> #include <chrono> #include <random> #include <bitset> //#include <atcoder/all> #define rep(i,n) for(int i=0;i<(n);i++) #define all(x) x.begin(), x.end() #define rall(x) x.rbegin(), x.rend() #define sz(x) ((int)(x).size()) #define pb push_back using ll = long long; using namespace std; template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; } template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; } ll gcd(ll a, ll b) {return b?gcd(b,a%b):a;} ll lcm(ll a, ll b) {return a/gcd(a,b)*b;} int main(){ ll H,W,N,K; cin >> H >> W >> N >> K; K--; if((H*W+1)%N==K) cout << "YES" << endl; else cout << "NO" << endl; return 0; }