#include <vector>
#include <cstdio>
#include <algorithm>
using namespace std;
using ll = long long int;
const ll LONGINF = 1LL << 60;

int main() {
    int N; scanf("%d", &N);
    N <<= 1;
    
    vector<ll> A(N), L(N+1), R(N+1);
    for(int i=0; i<N; i++) {
        scanf("%lld", &A[i]);
        L[i+1] = L[i] + (i % 2 ? -A[i] : A[i]);
        R[i+1] = R[i] + (i % 2 ? A[i] : -A[i]);
    }

    ll ans = -LONGINF;
    for(int i=0; i<=N; i+=2) {
        ans = max(ans, L[i] + (R[N] - R[i]));
    }
    printf("%lld\n", ans);
    return 0;
}