#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
#define DUMP(x) cout << #x << " = " << (x) << endl;
#define FOR(i, m, n) for (ll i = m; i < n; i++)
#define IFOR(i, m, n) for (ll i = n - 1; i >= m; i--)
#define REP(i, n) FOR(i, 0, n)
#define IREP(i, n) IFOR(i, 0, n)
#define FOREACH(x, a) for (auto&(x) : (a))
#define ALL(v) (v).begin(), (v).end()
#define SZ(x) ll(x.size())

int main() {
  ll n;
  cin >> n;
  ll a = 0, b = 0;
  REP(i, n - 1) {
    ll x, y;
    cin >> x >> y;
    a += x;
    b += y;
  }
  ll ans = 0;
  REP(i, b + 1) {
    ll t = i + a - b;
    if (t >= 0 && t <= a) ans++;
  }
  cout << ans << endl;
}