#include <bits/stdc++.h>
using namespace std;
#define modulo 998244353
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 1000000000000000000




int main(){
	
	int N;
	cin>>N;
	
	
	int sumA=0,sumB=0;
	vector<int> A(N-1),B(N-1);
	for(int i=0;i<N-1;i++){
		cin>>A[i]>>B[i];
		sumA += A[i];
		sumB += B[i];
	}
	
	
	int AA,BB;
	if(A>B){
		AA=0;
		BB=sumA-sumB;
		sumB+=BB;
	}
	else{
		AA=sumB-sumA;
		BB=0;
		sumA+=AA;
	}
	
	int ans = 0;
	
	while(true){
		bool f = true;
		for(int i=0;i<N-1;i++){
			if(A[i]>sumB-B[i]||B[i]>sumA-A[i]){
				AA++;
				BB++;
				sumA++;
				sumB++;
				f=false;
				break;
			}
		}
		if(!f)continue;
		if(AA>sumB-BB||BB>sumA-AA){
			break;
		}
		ans++;
		AA++;
		BB++;
		sumA++;
		sumB++;
	}
	cout<<ans<<endl;
		
	
    return 0;
}