#include<bits/stdc++.h>
using namespace std;
using ll = long long;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define ALL(v) (v).begin(), (v).end()
#define p(s) cout<<(s)<<endl
#define p2(s, t) cout << (s) << " " << (t) << endl
#define br() p("")
#define pn(s) cout << (#s) << " " << (s) << endl
#define p_yes() p("Yes")
#define p_no() p("No")

const ll mod = 1e9 + 7;
const ll inf = 1e18;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);

    // input
    ll N, K;
    cin >> N >> K;

    ll ma = N*(N+1)/2;
    ll mi = -ma + 2 * (N-K)*(N-K+1)/2;

    ll diff = ma - mi;
    ll step = diff/2;

    ll number_of_terms = step + 1;
    p(number_of_terms);
    
    return 0;
}