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

const long long INF = (1LL << 60);

int main() {
    int N;
    cin >> N;
    vector A(N, 0LL);
    for(int i = 0; i < N; i++) cin >> A[i];
    if(0 <= *min_element(begin(A), end(A))) {
        cout << -1LL * *min_element(begin(A), end(A)) << endl;
        return 0;
    }
    vector dp(N+1, vector(2, -INF));
    dp[0][0] = 0LL;
    for(int i = 0; i < N; i++) {
        for(int j = 0; j < 2; j++) {
            dp[i+1][j] = max(dp[i][j], dp[i+1][j]);
            if(((j) && (A[i] < 0)) || ((!j) && (0 <= A[i]))) continue;
            dp[i+1][1-j] = max(dp[i][j] + (j ? 1LL : -1LL) * A[i], dp[i+1][1-j]);
        }
    }
    cout << max(dp[N][0], dp[N][1]) << endl;
    return 0;
}