#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
#include<bits/stdc++.h>
using namespace std;
#define rep(i,s,t) for(ll i = (ll)(s); i < (ll)(t); i++)
#define rrep(i,s,t) for(ll i = (ll)(s-1);(ll)(t) <= i; i--)
#define all(x) (x).begin(), (x).end()
typedef long long ll;
typedef long double ld;
typedef pair<ll,ll> Pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
constexpr ll INF = numeric_limits<ll>::max()/4;
constexpr ll n_max = 2e5+10;
#define int ll
const long double pi = 3.14159265358979323846;

template <typename A, typename B>
string to_string(pair<A, B> p);
string to_string(const string &s) {return '"' + s + '"';}
string to_string(const char *c) {return to_string((string) c);}
string to_string(bool b) {return (b ? "true" : "false");}
template <size_t N>
string to_string(bitset<N> v){
    string res = "";
    for(size_t i = 0; i < N; i++) res += static_cast<char>('0' + v[i]);
    return res;
}
template <typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for(const auto &x : v) {
        if(!first) res += ", ";
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p){return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";}

void debug_out() {cerr << endl;}
template<typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}

#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

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

signed main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    ll n; cin >> n;
    ll ans = 0;
    rep(i,0,n){
        ll a,b; cin >> a >> b;
        ans += (a + b) * (b - a + 1) / 2;
    }

    cout << ans << endl;
}

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

int main()
{
  ios_base::sync_with_stdio(false);
   cin.tie(NULL);
  int t=1;
  //cin>>t;
  while(t--){
        ll n,k;
        cin>>n>>k;
        vector<ll>a(n);
     map<ll,ll>mp;
        for(int i=0;i<n;i++){
        cin>>a[i];
        mp[a[i]]++;
      }
        ll res=0;

      while(mp[0]>0 && k>0){
               ll pre=0;
           for(auto x:mp ){
              if( x.second>0 ){

                 if(pre ==x.first )
                       pre++;
                      else
                       break;
                        mp[x.first]--;
                           }
               else
                break;
              }
                 if(pre==0)
                 break;
                 else
                 res+=pre;
                 k--;
      }

      cout<<res;
  }
	return 0;
}
