#ifdef NACHIA
#define _GLIBCXX_DEBUG
#else
#define NDEBUG
#endif
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <utility>
#include <queue>
#include <array>
#include <cmath>
#include <atcoder/modint>

namespace nachia{

int Popcount(unsigned long long c) noexcept {
#ifdef __GNUC__
    return __builtin_popcountll(c);
#else
    c = (c & (~0ull/3)) + ((c >> 1) & (~0ull/3));
    c = (c & (~0ull/5)) + ((c >> 2) & (~0ull/5));
    c = (c & (~0ull/17)) + ((c >> 4) & (~0ull/17));
    c = (c * (~0ull/257)) >> 56;
    return c;
#endif
}

// please ensure x != 0
int MsbIndex(unsigned long long x) noexcept {
#ifdef __GNUC__
    return 63 - __builtin_clzll(x);
#else
    using u64 = unsigned long long;
    int q = (x >> 32) ? 32 : 0;
    auto m = x >> q;
    constexpr u64 hi = 0x8888'8888;
    constexpr u64 mi = 0x1111'1111;
    m = (((m | ~(hi - (m & ~hi))) & hi) * mi) >> 35;
    m = (((m | ~(hi - (x & ~hi))) & hi) * mi) >> 31;
    q += (m & 0xf) << 2;
    q += 0x3333'3333'2222'1100 >> (((x >> q) & 0xf) << 2) & 0xf;
    return q;
#endif
}

// please ensure x != 0
int LsbIndex(unsigned long long x) noexcept {
#ifdef __GNUC__
    return __builtin_ctzll(x);
#else
    return MsbIndex(x & -x);
#endif
}

}


namespace nachia {

struct DsuFast{
private:
    std::vector<int> w;
public:
    DsuFast(int n = 0) : w(n, -1) {}
    int leader(int u){
        if(w[u] < 0) return u;
        return w[u] = leader(w[u]);
    }
    int operator[](int u){ return leader(u); }
    int merge(int u, int v){
        u = leader(u);
        v = leader(v);
        if(u == v) return u;
        if(-w[u] < -w[v]) std::swap(u, v);
        w[u] += w[v];
        w[v] = u;
        return u;
    }
    int size(int u){ return -w[leader(u)]; }
    bool same(int u, int v){ return leader(u) == leader(v); }
};

} // namespace nachia

namespace nachia {

struct DecrementalPredecessorQuery{
private:
    int n;
    int b;
    std::vector<unsigned long long> X;
    nachia::DsuFast Y;
    std::vector<int> dsuTrans;
    int smallQ(int c, int d) const noexcept {
        auto z = X[c] & ((~0ull) << d);
        return z ? c*64 + LsbIndex(z) : -1;
    }
    int largeQ(int c) noexcept { return dsuTrans[Y.leader(c)]; }
public:
    DecrementalPredecessorQuery(int _n)
        : n(_n+2), b(n/64+2), X(b, ~0ull), Y(b), dsuTrans(b)
    {
        for(int i=0; i<b; i++) dsuTrans[i] = i;
    }
    // remove token i
    void dec(int i){
        i++;
        int c = i/64, d = i%64;
        X[c] &= ~(1ull << d);
        if(X[c] == 0){
            int h = largeQ(c+1);
            dsuTrans[Y.merge(c, c+1)] = h;
        }
    }
    // minimum token left x : i <= x
    int queryNoLessThan(int i){
        if(n <= i) return n;
        if(i < 0) i = 0;
        i++;
        int c = i/64, d = i%64;
        int x = smallQ(c, d);
        if(x >= 0) return x-1;
        c = largeQ(c+1); d = 0;
        return smallQ(c, d)-1;
    }
};

} // namespace nachia
using i64 = long long;
using u64 = unsigned long long;
#define rep(i,n) for(i64 i=0; i<(i64)(n); i++)
#define repr(i,n) for(i64 i=(i64)(n)-1; i>=0; i--)
const i64 INF = 1001001001001001001;
const char* yn(bool x){ return x ? "Yes" : "No"; }
template<typename A> void chmin(A& l, const A& r){ if(r < l) l = r; }
template<typename A> void chmax(A& l, const A& r){ if(l < r) l = r; }
template<typename A> using nega_queue = std::priority_queue<A,std::vector<A>,std::greater<A>>;
using Modint = atcoder::static_modint<998244353>;
using namespace std;

void testcase(){
    i64 N; cin >> N;
    vector<pair<i64,i64>> A(N);
    for(auto& [r,l] : A){ cin >> l >> r; l--; r--; }
    sort(A.begin(), A.end());
    i64 x = INF;
    rep(i,N) chmin(x, A[i].first - i);
    auto f = [&](i64 k) -> bool {
        auto dec = nachia::DecrementalPredecessorQuery(N);
        for(auto [r,l] : A){
            i64 q = dec.queryNoLessThan(l - k);
            if(N <= q || r < q+k) return false;
            dec.dec(q);
        }
        return true;
    };
    i64 ansL = x; {
        i64 ok = x;
        i64 ng = -1;
        while(ng + 1 < ok){
            i64 k = ng + (ok - ng) / 2;
            (f(k) ? ok : ng) = k;
        }
        ansL = ok;
    }
    i64 ansR = x-1; {
        i64 ok = x-1;
        i64 ng = INF;
        while(ok + 1 < ng){
            i64 k = ok + (ng - ok) / 2;
            (f(k) ? ok : ng) = k;
        }
        ansR = ok;
    }
    i64 ans = ansR - ansL + 1;
    cout << ans << endl;
}

int main(){
    ios::sync_with_stdio(false); cin.tie(nullptr);
    #ifdef NACHIA
    int T; cin >> T; for(int t=0; t<T; T!=++t?(cout<<'\n'),0:0)
    #endif
    testcase();
    return 0;
}