#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) begin(v),end(v)
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
using ll = long long;
using pii = pair<int, int>;
constexpr ll INF = 1ll<<30;
constexpr ll longINF = 1ll<<60;
constexpr ll MOD = 1000000007;
constexpr bool debug = false;
//---------------------------------//

int main() {
	int N;
	cin >> N;
	vector<int> A(2 * N);
	REP(i, 2 * N) scanf("%d", &A[i]);
	
	vector<ll> sum(N + 1);
	REP(i, N) sum[i + 1] = sum[i] + A[i * 2] - A[i * 2 + 1];
	
	ll ans = -longINF;
	REP(i, N + 1) {
		ll cur = sum[i];
		cur -= sum[N] - sum[i];
		chmax(ans, cur);
	}
	cout << ans << endl;
}