#pragma region
#pragma GCC target("avx2")
#pragma GCC optimize("03")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std; typedef long double ld; typedef long long ll;
typedef unsigned long long ull;
#define endl "\n"
#define FOR(i,a,b) for(int i=(a);i<=(b);i++)
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define ALL(x) (x).begin(), (x).end()
constexpr int INF=1<<30; constexpr ll LINF=1LL<<60; constexpr ll mod=1e9+7; constexpr int NIL = -1;
template<class T>inline bool chmax(T &a, const T &b) { if (a<b) { a = b; return 1; } return 0; }
template<class T>inline bool chmin(T &a, const T &b) { if (b<a) { a = b; return 1; } return 0; }
#pragma endregion
//-------------------
constexpr int MX = 1e+3;
int a[MX];
int b[MX];

int main(){
    cin.tie(0); ios::sync_with_stdio(false); //cout << fixed << setprecision(15);
    int n; cin >> n;
    int a_sm = 0, b_sm = 0;
    rep(i,1,n) {
        cin >> a[i] >> b[i];
        a_sm += a[i];
        b_sm += b[i];          
    }

    int cnt = 0;
    FOR(i,0,b_sm) {
        if(i+a_sm < b_sm) continue;
        int cursm = i+a_sm;
        a[0] = i;
        b[0] = cursm - b_sm; 
        bool ok = true;
        rep(i,0,n) {
            if(a[i] > cursm - b[i]) ok = false;
        }
        if(ok) cnt++;
    }
    cout << cnt << endl;
    return 0;
}