#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int n,k;
  cin>>n>>k;
  Int x=(n+1)*n/2;
  Int y=(n-k+1+n)*k/2;
  Int z=x-2*y;
  cout<<((x-z)/2+1)<<endl;
  return 0;
}