Codeforces Round #541 (Div. 2) B. Draw!(思维)

#include <bits/stdc++.h>
#define ll long long
#define maxn 10005
using namespace std;
int n,m;
struct Node{
  ll x,y;
}Edge[maxn];

int main()
{
  scanf("%d",&n);
  for(int i=1;i<=n;i++){
    cin>>Edge[i].x>>Edge[i].y;
  }
  ll a = 0, b = 0;
  ll ans = 1;
  for(int i=1;i<=n;i++){
    ans += max(0LL, min(Edge[i].x, Edge[i].y) - max(a, b) + 1);
    if(a == b) ans --;
    a = Edge[i].x;
    b = Edge[i].y;
  }
  cout<<ans<<endl;
  return 0;
}