#include <cstdio>

int main(void)
{
	int h, w, n, k;
	int no = 1;

	scanf("%d%d%d%d", &h, &w, &n, &k);
	
	int **math = new int*[h];
	for (int i = 0; i < h; i++)
	{
		math[i] = new int[w];
	}

	for (int i = 0; i < h; i++)
	{
		for (int j = 0; j < w; j++)
		{
			math[i][j] = no;
			if (no == n)
			{
				no = 1;
			}
			no++;
		}
	}

	if (math[h - 1][w - 1] == k)
	{
		printf("YES\n");
	}
	else
	{
		printf("NO\n");
	}

	return 0;
}