#include <bits/stdc++.h>
using namespace std;

int main() {
    int n;
    cin >> n;

    int maxInDeg = 0;
    int inQueue = 0; // ->
    int outQueue = 0; // <-
    for (int i = 0; i < n-1; ++i){
        int in, out;
        cin >> in >> out;
        maxInDeg += out;

        int deltaInQueue = min(inQueue, out);
        int deltaOutQueue = min(outQueue, in);
        inQueue -= deltaInQueue;
        outQueue -= deltaOutQueue;
        inQueue += out - deltaInQueue;
        outQueue += in - deltaOutQueue;
    }
    int ans = maxInDeg - abs(inQueue - outQueue) + 1;
    // cout << maxInDeg << ' ' << inQueue << ' ' << outQueue << endl;
    cout << ans << endl;
}