#include <iostream> #include <vector> #include <string> #include <stack> #include <queue> #include <deque> #include <set> #include <map> #include <algorithm> // require sort next_permutation count __gcd reverse etc. #include <cstdlib> // require abs exit atof atoi #include <cstdio> // require scanf printf #include <functional> #include <numeric> // require accumulate #include <cmath> // require fabs #include <climits> #include <limits> #include <cfloat> #include <iomanip> // require setw #include <sstream> // require stringstream #include <cstring> // require memset #include <cctype> // require tolower, toupper #include <fstream> // require freopen #include <ctime> // require srand #define rep(i,n) for(int i=0;i<(n);i++) #define ALL(A) A.begin(), A.end() #define each(i,c) for(auto i=(c).begin();i!=(c).end();++i) #define exist(s,e) ((s).find(e)!=(s).end()) #define clr(a) memset((a),0,sizeof(a)) #define nclr(a) memset((a),-1,sizoef(a)) #define sz(s) (int)((s).size()) #define INRANGE(x,s,e) ((s)<=(x) && (x)<(e)) #define pb push_back #define MP(x,y) make_pair((x),(y)) using namespace std; typedef long long ll; typedef pair<int, int> P; int main() { ios_base::sync_with_stdio(0); ll H, W, N, K; cin >> H >> W >> N >> K; cout << ((H*W - 1LL)%N == K - 1 ? "YES" : "NO" ) << endl; return 0; }