#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;
    int in=0, out=0;
    rep(i,n-1){
        int a,b; cin>>a>>b;
        in += a;
        out += b;
    }
    if(in > out){
        int sa = in - out;
        cout<<in - sa + 1<<endl;
    }else if(in == out){
        cout<<in + 1<<endl;
    }else{
        int sa = out - in;
        cout<<out - sa + 1<<endl;
    }
}