#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T, class U> using Pa = pair<T, U>;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    vec<ll> A(2*N);
    for(int i=0;i<2*N;i++) cin >> A[i];
    ll now = 0;
    for(int i=2*N-1;i>=0;i--){
        if(i%2) now += A[i];
        else now -= A[i];
    }
    ll ans = now;
    for(int i=0;i<2*N;i+=2){
        now += 2*A[i];
        now -= 2*A[i+1];
        ans = max(ans,now);
    }
    cout << ans << "\n";
}