#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cassert>
#include<cmath>
#include<ctime>
#include<iomanip>
#include<numeric>
#include<stack>
#include<queue>
#include<map>
#include<unordered_map>
#include<set>
#include<unordered_set>
#include<bitset>
#include<random>
using namespace std;
int N,A[2 << 17];
long long S[1 << 17];
void solve()
{
	cin >> N;
	for(int i = 0;i < 2*N;i++) cin >> A[i];
	for(int i = 0;i < N;i++) S[i+1] = S[i] + A[i*2]-A[i*2+1];
	long long ans = -(long long)1e18;
	for(int i = 0;i <= N;i++) ans = max(ans,S[i] + S[i] - S[N]);
	cout << ans << endl;
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	//cin >> tt;
	while(tt--) solve();
}