#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
template<class T> using VVV = V<VV<T>>;
template<class T> using VVVV = VV<VV<T>>;
#define rep(i,n) for(ll i=0ll;i<n;i++)
#define REP(i,a,n) for(ll i=a;i<n;i++)
const long long INF = (1LL << 60);
const long long mod99 = 998244353;
const long long mod107 = 1000000007;
const long long mod = mod99;
#define eb emplace_back
#define pb eb
#define be(v) (v).begin(),(v).end()
#define all(i,v) for(auto& i : v)
#define all2(i,j,v) for(auto& [i,j] : v)
template<class T, class U> void chmin(T& t, const U& u) { if (t > u) t = u; }
template<class T, class U> void chmax(T& t, const U& u) { if (t < u) t = u; }

// cin.tie(nullptr);
// ios::sync_with_stdio(false);
// cout << fixed << setprecision(20);

void solve(){
  ll n;
  cin >> n;
  V<ll> l(n), r(n);
  rep(i, n){
    cin >> l[i] >> r[i];
    l[i]--;
  }
  V<pair<ll,ll>> v,w;
  rep(i, n){
    v.eb(l[i], r[i]);
    w.eb(r[i], l[i]);
  }
  sort(be(v));
  sort(be(w));
  ll L = 0, R=INF;
  rep(i, n){
    auto[x,y] = v[i];
    chmax(L, x-i);
    auto[p,q] = w[i];
    chmin(R, p-i);
  }
  
  if(R >= L){
    cout << 0 << endl;
    return;
  }
  
  ll id = 0;
  multiset<ll> st;
  rep(i, n){
    while(id < n){
      auto[a,b] = v[id];
      if(i+L < a) break;
      st.insert(b);
      id++;
    }
    ll nd = *(st.begin());
    st.erase(st.begin());
    if(nd < i+L) continue;
    else R = -1;
  }
  
  
  cout << R-L << endl;
}





int main(){
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  int t=1;
  // cin >> t;
  rep(i,t) solve();
}