//#include <tourist>
#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
typedef long long ll;
typedef unsigned int uint;
typedef unsigned long long ull;
typedef pair<ll, ll> p;
const int INF = 1e9;
const ll LINF = ll(1e18);
const int MOD = 1000000007;
const int dx[4] = {0, 1, 0, -1}, dy[4] = {-1, 0, 1, 0};
const int Dx[8] = {0, 1, 1, 1, 0, -1, -1, -1}, Dy[8] = {-1, -1, 0, 1, 1, 1, 0, -1};
#define yes cout << "Yes" << endl
#define YES cout << "YES" << endl
#define no cout << "No" << endl
#define NO cout << "NO" << endl
#define rep(i, n) for (int i = 0; i < n; i++)
#define FOR(i, m, n) for (int i = m; i < n; i++)
#define ALL(v) v.begin(), v.end()
#define debug(v)          \
    cout << #v << ":";    \
    for (auto x : v)      \
    {                     \
        cout << x << ' '; \
    }                     \
    cout << endl;
template <class T>
bool chmax(T &a, const T &b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T &a, const T &b)
{
    if (b < a)
    {
        a = b;
        return 1;
    }
    return 0;
}
//cout<<fixed<<setprecision(15);有効数字15桁
//-std=c++14
//g++ yarudake.cpp -std=c++17 -I .
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }
int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll n;
    cin >> n;
    vector<ll> a(n), b(n);
    ll suma = 0;
    ll sumb = 0;
    rep(i, n - 1)
    {
        cin >> a[i] >> b[i];
        suma += a[i];
        sumb += b[i];
    }
    ll diff = suma - sumb;
    ll ans = 0;
    if (diff >= 0)
    {
        ll count = 0;
        while (true)
        {
            if (count > sumb || diff + count > suma)
            {
                break;
            }
            a[n - 1] = count;
            b[n - 1] = diff + count;
            rep(i, n)
            {
                if (sumb - b[i] + b[n - 1] < a[i])
                    break;
                if (i == n - 1)
                    ans++;
            }
            count++;
        }
    }
    else
    {
        ll count = 0;
        diff *= -1;
        while (true)
        {
            if (diff + count > sumb || count > suma)
            {
                break;
            }
            a[n - 1] = count + diff;
            b[n - 1] = count;
            rep(i, n)
            {
                if (sumb - b[i] + b[n - 1] < a[i])
                    break;
                if (i == n - 1)
                    ans++;
            }
            count++;
        }
    }
    cout<<ans<<"\n";
}