#include<bits/stdc++.h>
using namespace std;

#pragma GCC optimize("Ofast")

#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=r-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[8]={1,0,-1,0,1,1,-1,-1};
const ll dx[8]={0,1,0,-1,1,-1,1,-1};
template <typename T> inline bool chmax(T &a, T b) {
  return ((a < b) ? (a = b, true) : (false));
}
template <typename T> inline bool chmin(T &a, T b) {
  return ((a > b) ? (a = b, true) : (false));
}

int main(){
  set<ll> st;st.insert(0);
  ll n;cin >> n;
  while(n--){
    ll l,r;cin >> l >> r;
    set<ll> nst;
    bool flag=false;
    for(auto p:st){
      if(l<=p&&p<r){
        nst.insert(p+1);
      }
      else if(p>=r){
        if(!flag)flag=true;
        else nst.insert(p);
      }
      else nst.insert(p);
    }
    nst.insert(l);
    swap(st,nst);
  }
  cout << st.size()-1 << endl;
}