#include <bits/stdc++.h>

using namespace std;

using int64 = long long;
const int INF = 1 << 30;

struct UnionFind {
  vector< int > data;

  UnionFind(int sz) {
    data.assign(sz, -1);
  }

  bool unite(int x, int y) {
    x = find(x), y = find(y);
    if(x == y) return (false);
    if(data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return (true);
  }

  int find(int k) {
    if(data[k] < 0) return (k);
    return (data[k] = find(data[k]));
  }

  int size(int k) {
    return (-data[find(k)]);
  }
};

int main() {
  int N, A[100000], B[100000];
  int64 in[100001] = {}, out[100001] = {};
  UnionFind uf(100001);
  cin >> N;
  int low = INF;
  for(int i = 0; i < N; i++) {
    cin >> A[i] >> B[i];
    out[A[i]]++;
    in[B[i]]++;
    low = min(low, B[i]);
    uf.unite(A[i], B[i]);
  }
  int64 up[100002] = {}, down[100002] = {}; //i-1 ↔ i
  for(int i = 100000; i > low; i--) {
    up[i] = max((up[i + 1] + out[i]) - (down[i + 1] + in[i]), 0LL);
    down[i] = max((down[i + 1] + in[i]) - (up[i + 1] + out[i]), 0LL);
    if(up[i] > 0 || down[i] > 0) uf.unite(i - 1, i);
  }
  for(int i = 100000; i > low; i--) {
    if(uf.find(i) != uf.find(i - 1)) {
      uf.unite(i, i - 1);
      assert(up[i] == 0 && down[i] == 0);
      up[i] = down[i] = 1;
    }
  }

  auto check = [&](int left) {
    for(int i = left; i <= 100000; i++) up[i]--;
    UnionFind uf2(100001);
    for(int i = 0; i < N; i++) uf2.unite(A[i], B[i]);
    for(int i = 100000; i > low; i--) {
      if(up[i] > 0 || down[i] > 0) uf2.unite(i - 1, i);
    }
    int par = uf2.find(100000);
    bool f = true;
    for(int i = 0; i < N; i++) f &= uf2.find(A[i]) == par;
    for(int i = left; i <= 100000; i++) up[i]++;
    return f;
  };

  int ok = 100001, ng = low;
  while(ok - ng > 1) {
    int mid = (ok + ng) / 2;
    if(check(mid)) ok = mid;
    else ng = mid;
  }

  int64 all = 0;
  for(int i = ok; i <= 100000; i++) up[i]--;
  for(int i = 0; i <= 100000; i++) all += up[i];
  cout << all << endl;
}