#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, as = 0, bs = 0;
    cin >> n;
    for (int i = 0; i < n - 1; i++)
    {
        int a, b;
        cin >> a >> b;
        as += a;
        bs += b;
    }
    int ans = 0;
    for (int x = 0; x <= bs; x++)
    {
        int y = as + x - bs;
        if (y >= 0 && y <= as)
        {
            ans++;
        }
    }
    cout << ans << endl;
}

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