#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<long long,long long> pll;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
constexpr int mod=1000000007;
constexpr int mod1=998244353;
vector<int> dx={0,1,0,-1},dy={-1,0,1,0};
bool inside(int y,int x,int h,int w){
	if(y<h && y>=0 && x<w && x>=0) return true;
	return false;
}





int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n;cin >> n;
	ll sum1 = 0, sum2 = 0;
	rep(i,n - 1){
		int a,b;cin >> a >> b;
		sum1 += a;
		sum2 += b;
	}
	cout << max(sum2 - max((sum2 - sum1), 0LL), 0LL) + 1 << endl;
}