#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < n; ++i)
#define ALL(c) (c).begin(), (c).end()
#define SUM(x) std::accumulate(ALL(x), 0LL)
#define MIN(v) *std::min_element(v.begin(), v.end())
#define MAX(v) *std::max_element(v.begin(), v.end())
#define EXIST(v, x) (std::find(v.begin(), v.end(), x) != v.end())
using namespace std;

typedef long long ll;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
const int INF = 1e9;
const long long INFL = 1LL<<60;

int main()
{
  int n;
  cin >> n;
  if (n == 2) {
    cout << 1 << endl;
    return 0;
  }

  ll suma = 0;
  ll sumb = 0;
  ll maxa = 0;
  ll maxb = 0;
  rep(i, n-1) {
    ll a, b;
    cin >> a >> b;
    suma += a;
    sumb += b;
    chmax(maxa, a);
    chmax(maxb, b);
  }

  if (suma > sumb) {
    ll ans = 0;
    ll b = max(suma - sumb, 2 * maxb - sumb);
    for (; b - (suma - sumb) <= sumb; b++) {
      ans++;
    }
    cout << ans << endl;
    return 0;
  } else {
    ll ans = 0;
    ll a = max(sumb - suma, 2 * maxa - suma);
    for (; a - (sumb - suma) <= suma; a++) {
      ans++;
    }
    cout << ans << endl;
    return 0;
  }
}