#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i,n) for(int (i)=0;(i)<(n);(i)++)
#define rrep(i,n) for(int (i)=((n)-1);(i)>=0;(i)--)
#define itn int
#define all(x) (x).begin(),(x).end()
#define F first
#define S second
const long long INF = 1LL << 60;
const int MOD = 1000000007;
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
signed main(void){
    int n; cin>>n;
    vector <int> a(n);
    vector <int> b(n);
    int suma = 0, sumb = 0;
    rep(i,n-1){
        cin>>a[i+1]>>b[i+1];
        suma += a[i+1], sumb += b[i+1];
    }
    
    int ans = 0;
    for(int i=0;i<=sumb;i++){
        bool ok = true;
        a[0] = i;
        b[0] = suma + a[0] - sumb;
        if(b[0] < 0) ok = false;
        /*int Asum = accumulate(all(a),0), Bsum = accumulate(all(b),0);
        for(int j=0;j<n;j++){
            if(a[j] > Bsum - b[j] || b[j] > Asum - a[j]) ok = false;
        }*/
        if(ok) ans++;
    }
    cout<<ans<<endl;
}