#include <bits/stdc++.h>
using namespace std;
#if __has_include(<atcoder/all>)
#include <atcoder/all>
using namespace atcoder;
template<int mod>istream &operator>>(istream &is,static_modint<mod> &a){long long b;is>>b;a=b;return is;}
istream &operator>>(istream &is,modint &a){long long b;cin>>b;a=b;return is;}
#endif
#ifdef LOCAL
#include "debug.h"
#else
#define debug(...) static_cast<void>(0)
#define debugg(...) static_cast<void>(0)
template<typename T1,typename T2>ostream &operator<<(ostream &os,const pair<T1,T2>&p){os<<p.first<<' '<<p.second;return os;}
#endif
using ll=long long;
using ull=unsigned long long;
using P=pair<ll,ll>;
template<typename T>using minque=priority_queue<T,vector<T>,greater<T>>;
template<typename T>bool chmax(T &a,const T &b){return (a<b?(a=b,true):false);}
template<typename T>bool chmin(T &a,const T &b){return (a>b?(a=b,true):false);}
template<typename T1,typename T2>istream &operator>>(istream &is,pair<T1,T2>&p){is>>p.first>>p.second;return is;}
template<typename T>istream &operator>>(istream &is,vector<T> &a){for(auto &i:a)is>>i;return is;}
template<typename T1,typename T2>void operator++(pair<T1,T2>&a,int n){a.first++,a.second++;}
template<typename T1,typename T2>void operator--(pair<T1,T2>&a,int n){a.first--,a.second--;}
template<typename T>void operator++(vector<T>&a,int n){for(auto &i:a)i++;}
template<typename T>void operator--(vector<T>&a,int n){for(auto &i:a)i--;}
#define reps(i,a,n) for(int i=(a);i<(n);i++)
#define rep(i,n) reps(i,0,n)
#define all(x) x.begin(),x.end()
#define pcnt(x) __builtin_popcountll(x)
ll myceil(ll a,ll b){return (a+b-1)/b;}
template<typename T,size_t n,size_t id=0>
auto vec(const int (&d)[n],const T &init=T()){
  if constexpr (id<n)return vector(d[id],vec<T,n,id+1>(d,init));
  else return init;
}
void SOLVE();
int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  cout<<fixed<<setprecision(16);
  #ifdef LOCAL
  clock_t start=clock();
  #endif
  int testcase=1;
  //cin>>testcase;
  for(int i=0;i<testcase;i++){
    SOLVE();
  }
  #ifdef LOCAL
  cerr<<"time:";
  cerr<<(clock()-start)/1000;
  cerr<<"ms\n";
  #endif
}
void SOLVE(){
  int n;
  cin>>n;
  vector<P>a(n);
  cin>>a;
  a--;
  ll ok=-1e10,ng=1e10;
  while(ng-ok>1){
    ll mid=(ok+ng)/2;
    vector<int>cnt(n,0);
    bool f=true;
    rep(i,n){
      if(a[i].second-mid<0)f=false;
      else cnt[min<ll>(n-1,a[i].second-mid)]++;
    }
    if(cnt[0]>1)f=false;
    reps(i,1,n){
      cnt[i]+=cnt[i-1];
      if(cnt[i]>i+1)f=false;
    }
    (f?ok:ng)=mid;
  }
  ll mx=ok;
  ok=1e10,ng=-1e10;
  while(ok-ng>1){
    ll mid=(ok+ng)/2;
    vector<int>cnt(n,0);
    bool f=true;
    rep(i,n){
      if(a[i].first-mid>=n)f=false;
      else cnt[max<ll>(0,a[i].first-mid)]++;
    }
    if(cnt[n-1]>1)f=false;
    for(int i=n-2;i>=0;i--){
      cnt[i]+=cnt[i+1];
      if(cnt[i]>n-i)f=false;
    }
    (f?ok:ng)=mid;
  }
  ll mn=ok;
  debug(mn,mx);
  if(mx<mn)cout<<0<<endl;
  else cout<<mx-mn+1<<endl;
}