#include using namespace std; using uint = unsigned int; using ll = long long; using ull = unsigned long long; template using V = vector; template using VV = V>; template using VVV = V>; template using VVVV = VV>; #define rep(i,n) for(ll i=0ll;i void chmin(T& t, const U& u) { if (t > u) t = u; } template 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 l(n), r(n); rep(i, n){ cin >> l[i] >> r[i]; l[i]--; } V> 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 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(); }