#include <bits/stdc++.h>
using namespace std;
using ll = long long;

struct dsu {
    public:
    int csz;
    dsu() : _n(0) {}
    dsu(int n) : _n(n), csz(n), parent_or_size(n, -1) {}

    int merge(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        int x = leader(a), y = leader(b);
        if (x == y) return x;
        parent_or_size[x] = y;
        return y;
    }

    bool same(int a, int b) {
        assert(0 <= a && a < _n);
        assert(0 <= b && b < _n);
        return leader(a) == leader(b);
    }

    int leader(int a) {
        assert(0 <= a && a < _n);
        if (parent_or_size[a] < 0) return a;
        return parent_or_size[a] = leader(parent_or_size[a]);
    }

    int size(int a) {
        assert(0 <= a && a < _n);
        return -parent_or_size[leader(a)];
    }

    std::vector<std::vector<int>> groups() {
        std::vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++) {
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        std::vector<std::vector<int>> result(_n);
        for (int i = 0; i < _n; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            std::remove_if(result.begin(), result.end(),
                           [&](const std::vector<int>& v) { return v.empty(); }),
            result.end());
        return result;
    }

    private:
    int _n;
    // root node: -1 * component size
    // otherwise: parent
    std::vector<int> parent_or_size;
};

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    cin >> n;
    vector<pair<int,int>> b(n);
    vector<int> a(n);
    dsu uf(n);
    for(int i = 0; i < n; i++){
        cin >> a[i];
        b[i] = make_pair(a[i], i);
    }
    sort(a.rbegin(), a.rend());
    for(int i = 0; i < n; i++){
        int v, p;
        tie(v, p) = b[i];
        v = a[uf.leader(i)];
        if(p >= 1 && abs(v) < a[uf.leader(p - 1)]){
            uf.merge(p, uf.leader(p - 1));
            v = a[uf.leader(p)];
        }
        if(p + 1 < n && abs(v) < a[uf.leader(p + 1)]){
            uf.merge(p, uf.leader(p + 1));
        }
    }
    ll ans = 0;
    for(int i = 0; i < n; i++){
        ans += abs(a[uf.leader(i)]);
    }
    cout << ans << '\n';
}