#include "bits/stdc++.h"

using namespace std;

//------------------------------- Libraries --------------------------------//

//------------------------------- Type Names -------------------------------//

using i64 = int_fast64_t;

using seika = string;
//akari : 1D, yukari : 2D, maki : 3D vector
template <class kizuna>
using akari = vector<kizuna>;
template <class yuzuki>
using yukari = akari<akari<yuzuki>>;
template <class tsurumaki>
using maki = akari<yukari<tsurumaki>>;
//akane : ascending order, aoi : decending order
template <class kotonoha>
using akane = priority_queue<kotonoha, akari<kotonoha>, greater<kotonoha>>;
template <class kotonoha>
using aoi = priority_queue<kotonoha>;

//------------------------------- Dubug Functions ---------------------------//
inline void print()
{
    cout << endl;
}
template <typename First, typename... Rest>
void print(const First &first, const Rest &... rest)
{
    cout << first << ' ';
    print(rest...);
}
//------------------------------- Solver ------------------------------------//

void solve()
{
    int n, m1 = 0, m2 = 0;
    cin >> n;
    akari<int> as(n), bs(n);
    for (int i = 0; i < n - 1; i++)
    {
        cin >> as[i] >> bs[i];
        m1 += as[i];
        m2 += bs[i];
    }
    int ans = 0;
    for (int x = 0; x <= m2; x++)
    {
        int y = m1 + x - m2, f = y >= 0;
        for (int j = 0; j < n - 1; j++)
        {
            f &= as[j] <= m2 + y - bs[j];
        }
        ans += f;
    }
    cout << ans << endl;
}

int main()
{
    solve();
    return 0;
}