#include<bits/stdc++.h>
using namespace std;
 
#define int  long long
 
#define for1(i,m,n) for(int i=m;i<=n;i++)
#define for0(i,m,n) for(int i=m;i<n;i++)
#define vll(v) v.begin(),v.end()
 #define ii pair<int,int>
 #define se second
 #define fi first
 #define el '\n'
 
 const int N=1e2;
 const int mod=-25*1e5-11;
 
 signed main(){
   ios_base::sync_with_stdio(0);
   cin.tie(0);
   cout.tie(0);
 
   int n,k;cin>>n>>k;
   cout<<(int)1.0*n*(2+(n-1)*k)/2;
return 0;
 }
/*
3 4 1
1 2 -1 -1
1 -1 -1 -1
1 1 1 1
*/

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