#include <cstdio>
#include <cstring>
#include <cmath>
#include <cassert>
#include <random>
#include <vector>
#include <algorithm>
#include <array>
#include <functional>
#include <utility>
#include <regex>
#include <tuple>
#include <map>
#include <set>

using namespace std;

int main(){
	int64_t h,w,n,k;
	-scanf("%ld%ld%ld%ld",&h,&w,&n,&k);
	puts((h+w-2)%n+1==k?"YES":"NO");
	return 0;
}