#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}


struct FastIO{
  FastIO(){
    cin.tie(0);
    ios::sync_with_stdio(0);
  }
}fastio_beet;

//INSERT ABOVE HERE
signed main(){
  Int n;
  cin>>n;
  n--;
  vector<Int> as(n),bs(n);
  for(Int i=0;i<n;i++) cin>>as[i]>>bs[i];

  Int sa=0,sb=0;
  for(Int a:as) sa+=a;
  for(Int b:bs) sb+=b;

  Int in=0,out=0;
  for(Int i=0;i<n;i++){
    in +=max(0LL,bs[i]-(sa-as[i]));
    out+=max(0LL,as[i]-(sb-bs[i]));
  }
  if(sa<=sb){
    chmax(in,sb-sa);
    cout<<(sb-in+1)<<endl;
  }else{
    chmax(out,sa-sb);
    cout<<(sa-out+1)<<endl;
  }
  return 0;
}