#include<bits/stdc++.h>
using namespace std;
#define ll long long
typedef pair<ll,ll> P;
#define M 1000000007
int main(){
  int n,c=0,d=0,a,b;
  cin>>n;
  for(int i=1;i<n;i++){
    cin>>a>>b;
    c+=a;d+=b;
  }
  if(c>d)cout<<c-d <<endl;
  else cout<<d-c+1<<endl;
}