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

int main()
{
    int N;
    cin >> N;
    vector<long long> A(N);
    for (int i = 0; i < N; i++)
    {
        cin >> A[i];
    }
    vector<vector<long long>> dp(N + 1, vector<long long>(2));
    dp[0][0] = -A[0];
    dp[0][1] = 0;
    for (int i = 1; i <= N; i++)
    {
        if (A[i - 1] == 0)
        {
            dp[i][0] = max(dp[i - 1][1], dp[i][0]);
            dp[i][1] = max(dp[i - 1][0], dp[i][1]);
        }
        else if (A[i - 1] > 0)
        {
            dp[i][0] = max(dp[i - 1][0], max(dp[i - 1][1] - A[i - 1], -A[i - 1]));

            if (i != 1)
            {
                dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] + A[i - 1]);
            }
        }
        else if (A[i - 1] < 0)
        {
            dp[i][0] = max(dp[i - 1][0], max(dp[i - 1][1] - A[i - 1], -A[i - 1]));
            if (i != 1)
            {
                dp[i][1] = max(dp[i - 1][1], dp[i - 1][0] + A[i - 1]);
            }
        }
    }
    long long ans = -1e18;
    for (int i = 1; i <= N; i++)
    {
        for (int j = 0; j < 2; j++)
        {
            ans = max(ans, dp[i][j]);
        }
    }
    cout << ans;
}