#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using namespace std;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll mod=998244353;
ll inf=1009999999999999990;
int main(){
    ll n;
    cin >> n;
    vector<ll>a(2*n);
    for (ll i = 0; i < n*2; i++)
    {
        cin >> a[i];
    }
    vector<ll>b(n);
    for (ll i = 0; i < n; i++)
    {
        b[i]=a[i*2+1]-a[i*2];
        if (i>0)
        {
            b[i]+=b[i-1];
        }
    }
    ll ans=b[n-1];
    ll now=b[n-1];
    for (ll i = 0; i < n; i++)
    {
        now+=(a[i*2]-a[i*2+1])*2;
        ans=max(ans,now);
    }
    cout << ans << endl;
}