#include <bits/stdc++.h>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;


int main(){
  int N;
  cin >> N;
  
  vector<vector<int>> v;
  int S = 0, T = 0;
  rep(i,N-1){
    int a, b;
    cin >> a >> b;
    v.push_back({a,b});
    S += a;
    T += b;
  }

  int ret = 0;
  rep(x,20005){
    int y = x + S - T;
    if(y<0) continue;
    if(x>T) continue;
    ret++;
  }
  cout << ret << endl;
  
  return 0;
}