#include <bits/stdc++.h>
using namespace std;
const long long INF=1e18;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N; cin >> N;
    vector<long long> A(2*N);
    for (int i=0;i<2*N;++i) cin >> A[i];
    vector<long long> diffs(N+1,0);
    for (int i=0;i<N;++i) diffs[i+1]=A[2*i]-A[2*i+1];
    for (int i=0;i<N;++i) diffs[i+1]+=diffs[i];
    long long ans=-INF;
    for (int i=0;i<N+1;++i) ans=max(ans,diffs[i]*2-diffs[N]);
    cout << ans << '\n';
}