#include <bits/stdc++.h>
using namespace std;
#define ALL(a) (a).begin(),(a).end()
#define rALL(a) (a).rbegin(),(a).rend()
typedef pair<int, int> Pint;
typedef pair<int64_t, int64_t> Pll;

int main() {
    int64_t N, ans = -10000000000000000;
    cin >> N;
    vector<int64_t> A(2 * N), B(N), left(N), right(N);
    for (int i = 0; i < 2 * N; i++){
        cin >> A.at(i);
    }
    for (int i = 0; i < N; i++){
        B.at(i) = A.at(2 * i) - A.at(2 * i + 1);
    }
    for (int i = 0; i < N; i++){
        if (i == 0){
            left.at(i) = B.at(i);
            continue;
        }
        left.at(i) = left.at(i - 1) + B.at(i);
    }
    for (int i = 0; i < N; i++){
        if (i == 0){
            right.at(N - i - 1) = B.at(N - i - 1) * (-1);
            continue;
        }
        right.at(N - i - 1) = right.at(N - i) - B.at(N - i - 1);
    }
    for (int i = 0; i < N - 1; i++){
        ans = max(ans, right.at(i + 1) + left.at(i));
    }
    ans = max(ans, right.at(0));

    cout << ans << endl;

}