#include <stdio.h>
int main()
{
  int N,M,X,Y;
  scanf("%d %d",&N,&M);
  scanf("%d %d",&X,&Y);
  int X1,X2,XC;
  int Y1,Y2,YC;
  X1 = X/M;
  X2 = X%M;
  if (X1%2 == 0) {
    if (X2 == 0) {
      XC = 1;
    } else {
      XC = X2;
    }
  } else {
    if (X2 == 0) {
      XC = M;
    } else {
      XC = (M+1) - X2;
    }
  }
  Y1 = Y/M;
  Y2 = Y%M;
  if (Y1%2 == 0) {
    if (Y2 == 0) {
      YC = 1;
    } else {
      YC = Y2;
    }
  } else {
    if (Y2 == 0) {
      YC = M;
    } else {
      YC = (M+1) - Y2;
    }
  }
  if (XC == YC) {
    printf("YES\n");
  } else {
    printf("NO\n");
  }
  return 0;
}