Problem:
Score : 100 points

Problem Statement

Determine if we can choose K different integers between 1 and N (inclusive) so that no two of them differ by 1.

Constraints

1\leq N,K\leq 100

N and K are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

If we can choose K integers as above, print YES; otherwise, print NO.

Sample Input 1

3 2

Sample Output 1

YES

We can choose 1 and 3.

Sample Input 2

5 5

Sample Output 2

NO

Sample Input 3

31 10

Sample Output 3

YES

Sample Input 4

10 90

Sample Output 4

NO

Solution in C++14 (GCC 5.4.1) (judge verdict: Runtime Error)

#define _CRT_SECURE_NO_WARNINGS
#define forn(i, a, n) for(ll i = a; i < n; i++)

#include<iostream>
#include<string>
#include<vector>
#include<math.h>
#include<algorithm>
#include<set>
#include<map>
#include<queue>
#include<iomanip>
#include<cassert>
#include<stack>
#include<deque>
#include<list>
#include<sstream>
#include<unordered_map>
#include<time.h>
#include<functional>
#pragma comment(linker, "/STACK:8809999999")

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;
typedef pair<ld, ld> pld;
typedef pair<pll, ll> ppll;
typedef pair<pll, pll> ppp;
typedef vector<vector<vector<ll>>> vvv;
const ll mod = 1e9 + 7;
const ld eps = 1e-9;
const ll settled = 400007;



int main()
{
	ios_base::sync_with_stdio(false); cout.tie(NULL);
#ifndef overlord
	freopen("capitals.in", "r", stdin);
	freopen("capitals.out", "w", stdout);
#else
	/*freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);*/
#endif

	ll n, k;
	cin >> n >> k;
	ll sum = 0;
	forn(i, n, k)
	{
		forn(j, i + 1, k)
			sum++;
	}

	cout << sum;
	return 0;
}