#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
typedef signed long long ll;
#define ITR(i,c) for(auto i=begin(c);i!=end(c);i++)
#define FOR(i,a,n) for(int i=a;i<(int)(n);i++)
#define FORR(x,arr) for(auto& x:arr)
#define REP(i,n) FOR(i,0,n)
#define ALL(c) begin(c),end(c)
#define PB push_back
#define MP make_pair
const int DX[4]={0,1,0,-1}, DY[4]={-1,0,1,0};
const int INF = 1e9;

int main(int argc, char const *argv[]) {
    ll H,W,N,K;
    cin >> H >> W >> N >> K;
    ll t = W-1 + H-1 + 1;
    if(t%N==0) cout << (K==N?"YES":"NO") << endl;
    else cout << (t%N==K?"YES":"NO") << endl;
    return 0;
}