#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; ++i)
#define all(a) (a).begin(), (a).end()

int main() {
    cin.tie(nullptr);
    
    int N;
    cin >> N;
    vector<ll> A(2 * N), sum(N);
    rep(i, 0, 2 * N) cin >> A[i];
    
    rep(i, 0, N) sum[i] = A[2 * i] - A[2 * i + 1];
    rep(i, 1, N) sum[i] += sum[i - 1];
    
    ll ans = -sum[N - 1];
    rep(i, 0, N) {
        ll res = 2 * sum[i] - sum[N - 1];
        ans = max(res, ans);
    }
    
    cout << ans << '\n';
}