#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pb push_back
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define FORS(i,a,b) for(int i=(a);i<(b);++i)
#define PII pair<int,int>
#define vpp vector<PII>
#define all(x) x.begin(),b.end()
#define SZ(x) ((int)(x).size())
#define ll long long
#define maxn 10005

int n,sol,maxi,mini,ant;

int main()
{
    freopen("pluton.in","r",stdin);
    //freopen("pluton.out","w",stdout);
    cin>>n;
    PII t1,t2;
    cin>>t1.fi>>t1.se;
    sol=min(t1.fi,t1.se)+1;
    ant=sol-1;
    FORS(i,1,n){
        cin>>t2.fi>>t2.se;
        maxi=max(t1.fi,t1.se);
        mini=min(t2.fi,t2.se);
        if(t1.se==0&&t1.fi==0)maxi++;
        if(maxi<=mini&&ant!=mini)
            sol+=((mini!=maxi)?(mini-maxi+1):1);
        ant=mini;
        t1=t2;
    }
    cout<<sol;
}