#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";}



signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N;
	int sa = 0, sb = 0;
	int a1 = 0, a2 = 0, b1 = 0, b2 = 0;
	
	int maxa = -INF, maxb = -INF;
	cin>>N;
	
	for(int i = 1; i < N; i++){
		int a, b;
		
		cin>>a>>b;
		
		sa += a;
		sb += b;
		
		maxa = max(maxa, a-b);
		maxb = max(maxb, b-a);
	}
	
	maxa -= sb;
	maxb -= sa;
	
	
	a1 = max(0ll, maxa);
	b1 = max(0ll, maxb);
	
	a2 = sb;
	b2 = sa;
	
	a1 += sa - sb;
	a2 += sa - sb;
	
	// cout<<"a1 = "<<a1<<" a2 = "<<a2<<" b1 = "<<b1<<" b2 = "<<b2<<endl;
	
	cout<<max(min(a2, b2) - max(a1, b1) + 1, 0ll)<<endl;
	
	return 0;
}