#define _CRT_SECURE_NO_WARNINGS
#define _USE_MATH_DEFINES

#include <bits/stdc++.h>
using namespace std;
using i32 = int32_t;  using i64 = int64_t;  using str = string;
using u32 = uint32_t; using u64 = uint64_t; using usize = size_t;
using f64 = double_t; template <typename T> using vec = vector<T>;
#define times(n, i) for (i64 i = 0; i < (n); ++i)
#define range(n, m, i) for (i64 i = (n); i < (m); ++i)
#define upto(n, m, i) for (i64 i = (n); i <= (m); ++i)
#define downto(n, m, i) for (i64 i = (n); i >= (m); --i)
#define foreach(xs, x) for (auto &x : (xs))
#define all(xs) (xs).begin(), (xs).end()
#define sortall(xs) sort(all(xs))
#define reverseall(xs) reverse(all(xs))
#define uniqueall(xs) (xs).erase(unique(all(xs)), (xs).end())
#define maximum(xs) (*max_element(all(xs)))
#define minimum(xs) (*min_element(all(xs)))
#define even(x) (((x) & 1) == 0)
#define odd(x) (((x) & 1) == 1)
#define append emplace_back
const i64 MOD = 1000000007;

i64 h,w,n,k;

i32 main()
{
    cin >> h >> w >> n >> k;

    i64 turn = 1;
    if (w == 1) {
        w = h;
        h = 1;
    } else if (h == 1) {
        turn = w % n;
    } else {
        turn = (w + h - 1) % n;
    }

    i64 ans = 1;
    if (turn == 0)
        ans = n;
    else
        ans = turn;
    cout << (ans == k ? "YES" : "NO") << endl;
    return 0;
}