#include<deque> #include<queue> #include<vector> #include<algorithm> #include<iostream> #include<set> #include<cmath> #include<tuple> #include<string> #include<chrono> #include<functional> #include<iterator> #include<random> #include<unordered_set> #include<array> #include<map> #include<iomanip> #include<assert.h> #include<bitset> #include<stack> #include<memory> using namespace std; using namespace std::chrono; typedef long long int llint; typedef double lldo; #define mp make_pair #define mt make_tuple #define pub push_back #define puf push_front #define pob pop_back #define pof pop_front #define fir first #define sec second #define res resize #define ins insert #define era erase /*cout<<fixed<<setprecision(20);cin.tie(0);ios::sync_with_stdio(false);*/ const llint mod=1000000007; const llint big=2.19e15+1; const long double pai=3.141592653589793238462643383279502884197; const long double eps=1e-15; template <class T,class U>bool mineq(T& a,U b){if(a>b){a=b;return true;}return false;} template <class T,class U>bool maxeq(T& a,U b){if(a<b){a=b;return true;}return false;} llint gcd(llint a,llint b){if(a%b==0){return b;}else return gcd(b,a%b);} llint lcm(llint a,llint b){if(a==0){return b;}return a/gcd(a,b)*b;} template<class T> void SO(T& ve){sort(ve.begin(),ve.end());} template<class T> void REV(T& ve){reverse(ve.begin(),ve.end());} template<class T>llint LBI(vector<T>&ar,T in){return lower_bound(ar.begin(),ar.end(),in)-ar.begin();} template<class T>llint UBI(vector<T>&ar,T in){return upper_bound(ar.begin(),ar.end(),in)-ar.begin();} int main(void){ llint k,n;cin>>n>>k; cout<<(n+n-k+1)*k/2+1<<endl; return 0; }