#include <bits/stdc++.h>
#define ALL(x) (x).begin(), (x).end()
#define LB(v, x) (int)(lower_bound(ALL(v), x) - (v).begin())
#define UQ(v) sort(ALL(v)), (v).erase(unique(ALL(v)), (v).end())
#define IO ios::sync_with_stdio(false), cin.tie(nullptr);
#define chmax(a, b) (a) = (a) < (b) ? (b) : (a)
#define chmin(a, b) (a) = (a) < (b) ? (a) : (b)
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

int main() {
    int N;
    cin >> N;
    vector<ll> C(N);
    for (int i = 0; i < N; i++) cin >> C[i];

    if (C[0] >= 0) {
        cout << 2ll * C.back() << endl;
    } else if (C.back() <= 0) {
        cout << -2ll * C[0] << endl;
    } else {
        cout << 2ll * (C.back() - C[0]) << endl;
    }
}