#include <bits/stdc++.h>
//----***やべーやつら***----
using namespace std;

//----***型定義***----
using ll = long long;
using P = pair<ll,ll>;

//----***Like a Pythonista***----
#define REP(ii,jj,nn) for (ll ii=jj;ii<(nn);ii++)
#define RREP(ii,nn,jj) for (ll ii = nn; jj<ii;ii--)
#define each(i,...) for (auto&& i:__VA_ARGS__)
#define ALL(vec) (vec).begin(),(vec).end()
#define sum(...) accumulate(ALL(__VA_ARGS__),0LL)
#define dsum(...) accumulate(ALL(__VA_ARGS__),0.0)
#define vec(type,name,...) vector<type> name(__VA_ARGS__)
template<class T> inline auto max(const T& a){ return *max_element(ALL(a)); }
template<class T> inline auto min(const T& a){ return *min_element(ALL(a)); }
inline ll gcd(ll a,ll b){if(b == 0) return a;return  gcd(b,a%b);}
inline ll lcm(ll a,ll b){ll g = gcd(a,b);return a / g * b;}

//----***定数***----
#define MOD 1000000007
#define INF 100000000000000000
#define EPS 1e-9
#define PI  acos(-1)
const vector<vector<ll>> DXY={{-1,0},{1,0},{0,-1},{0,1}};

//----***パーツ***----
#define fi first
#define se second
#define pb push_back
#define re return
#define br break

//----***入出力***---
void print() { std::cout << "\n"; }
template <class T>void print(const T &x) {std::cout << x<<"\n";}
template <class T, class... Args>void print(const T &x, const Args &... args) {std::cout << x << " ";print(args...);}
#define debug(var)  do{std::cerr << #var << " ↓ "<<"\n";view(var);}while(0);
#define dbg cerr<<"🥺🥺🥺🥺🥺🥺"<<endl;
template<typename T> void view(T e){std::cout << e << std::endl;}
template<typename T> void view(const std::vector<T>& v){for(const auto& e : v){ std::cout << e << " "; } std::cout << std::endl;}
template<typename T> void view(const std::vector<std::vector<T> >& vv){ for(const auto& v : vv){ view(v); } }

//----***初期化時読み込み***----
struct initial{initial(){cin.tie(0); ios::sync_with_stdio(0); cout<<fixed<<setprecision(15);};}initial_;

int main(){
  int N;cin>>N;
  vector<vector<ll> > A(N,vector<ll>(2,0));
  ll ans=0;
  REP(i,0,N){
    cin>>A[i][0]>>A[i][1];
    ans+=((A[i][1]-A[i][0]+1)*(A[i][1]+A[i][0]))/2;
  }
  print(ans);


}

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())
#define endl "\n"
template<class T> void chmax(T &a, const T b){ a = max(a, b); }
template<class T> void chmin(T &a, const T b){ a = min(a, b); }
long long gcd(long long a, long long b) { return (a % b) ? gcd(b, a % b) : b; }
long long lcm(long long a, long long b) { return a / gcd(a, b) * b; }

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    ll x, y, z;
    cin >> x >> y >> z;
    cout << (y * z - 1) / x << endl;
    return 0;
}
