#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<climits>
#include<cmath>
#include<string>
#include<vector>
#include<set>
#include<map>
#include<queue>
#include<numeric>
#include<functional>
#include<algorithm>
#include<bitset>
#include<tuple>
#include<unordered_set>
#include<unordered_map>
#include<random>
#include<array>
#include<cassert>
using namespace std;
#define INF (1<<29)
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define uniq(v) v.erase(unique(all(v)),v.end())


int n;
int a[200000];
long long b[200001];

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);

	cin >> n;
	rep(i, n*2)cin >> a[i];

	b[2*n] = 0;
	for (int i = 2*n - 2; i >= 0; i -= 2) {
		b[i] = b[i + 2] + a[i + 1] - a[i];
	}
	long long ans = b[0], s = 0;
	for (int i = 0; i < 2 * n; i += 2) {
		s += a[i] - a[i + 1];
		ans = max(ans, s + b[i + 2]);
	}
	cout << ans << endl;


	return 0;
}