#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>

using namespace std;

#define int long long
#define endl "\n"

const long long INF = (long long)1e18;
const long long MOD = 1'000'000'007; 

string yn(bool f){return f?"Yes":"No";}
string YN(bool f){return f?"YES":"NO";}

#define a first
#define b second

signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N;
	int sa = 0, sb = 0;
	vector<pair<int,int>> x;
	int con = 0;
	cin>>N;
	
	x.resize(N);
	
	for(int i = 1; i < N; i++){
		// int a, b;
		
		cin>>x[i].a>>x[i].b;
		
		sa += x[i].a;
		sb += x[i].b;
		
	}
	
	for(int i = 0; i <= sa + sb; i++){
		int y = i + sa - sb;
		bool flag = true;
		int xa = sa + i, xb = sb + y;
		
		if(y < 0) continue;
		
		x[0].a = i;
		x[0].b = y;
		
		for(int j = 0; j < N; j++){
			if(x[j].a > xb - x[j].b || x[j].b > xa - x[j].a) {
				flag = false;
				break;
			}
		}
		
		if(flag) con++;
	}
	
	cout<<con<<endl;
	
	return 0;
}