import java.util.*;
import java.io.*;
import java.math.*;

class Main{

    static void solve(){

        int n = ni();
        long [] A = new long[n];
        for(int i = 0 ; i < n ; i ++ ) {
            A[i] = nl();
        }
        long [] dp = new long[n];
        Arrays.fill(dp,(long)-1e18);
        dp[0] = A[0];
        for(int i = 0 ;i < n-1 ; i++) {
            if(Math.abs(dp[i]) < Math.abs(A[i+1])) { //引き継がない
                dp[i+1] = Math.abs(A[i+1]);
            }
            else {
                dp[i+1] = dp[i];
            }
        }
        long ans = 0;
        for(int i = 0;i < n ; i++) ans += dp[i];
        output.print(ans);
    }

    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - //

    static int ni(){ return Integer.parseInt(sc.next()); }
    static long nl(){ return Long.parseLong(sc.next()); }
    static double nd(){ return Double.parseDouble(sc.next()); }
    static String ns(){ return sc.next(); }
    static BigInteger bi(){ return sc.nextBigInteger(); }
    static BigDecimal bd(){ return sc.nextBigDecimal(); }

    static PrintWriter output;
    static Scanner sc ;
    public static void main(String[] args){
        output = new PrintWriter(System.out);
        sc = new Scanner(System.in);
        solve();
        output.flush();
    }

}