#include <bits/stdc++.h>
using namespace std;

//repetition
#define FOR(i,a,b) for(ll i=(a);i<(b);++i)
#define rep(i, n) for(ll i = 0; i < (ll)(n); i++)

//container util
#define all(x) (x).begin(),(x).end()

//typedef
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VLL;
typedef vector<VLL> VVLL;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<ll, ll> PLL;

//const value
//const ll MOD = 1e9 + 7;
//const int dx[] = {0,1,0,-1};//{0,0,1,1,1,-1,-1,-1};
//const int dy[] = {1,0,-1,0};//{1,-1,0,1,-1,0,1,-1};

//conversion
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
inline ll toLL(string s) {ll v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}


int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  ll n;
  cin >> n;
  VLL a(n,0),b(n,0);
  rep(i,n-1) cin >> a[i] >> b[i];
  ll sumA = 0, sumB = 0;
  rep(i,n-1){
    sumA += a[i];
    sumB += b[i];
  }


  ll ans = 0;
  rep(b0,sumA+1){
    ll a0 = b0 + sumB - sumA;
    if(a0 <= sumB && a0 >= 0) ans++;
  }
  cout << ans << endl;

  return 0;
}