#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <cstring>
#include <queue>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <map>
#include <functional>
#include <cmath>
#include <cassert>
#include <string>
#include <iostream>

using namespace std;
typedef long long ll;
typedef pair<int, int> P;
//typedef pair<ll, ll> P;
ll MOD = 1000000007;
const int mod = 1000000007;
ll INF = 1LL << 60;

template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val)
{
   fill((T *)array, (T *)(array + N), val);
}



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

   ll n , k;
   cin >> n >> k;

   cout <<(k*(2*n-k+1))/2  +1<< endl;


}