Problem:
Score : 900 points

Problem Statement

Joisino has a formula consisting of N terms: A_1 op_1 A_2 ... op_{N-1} A_N.
Here, A_i is an integer, and op_i is an binary operator either + or -.
Because Joisino loves large numbers, she wants to maximize the evaluated value of the formula by inserting an arbitrary number of pairs of parentheses (possibly zero) into the formula.
Opening parentheses can only be inserted immediately before an integer, and closing parentheses can only be inserted immediately after an integer.
It is allowed to insert any number of parentheses at a position.
Your task is to write a program to find the maximum possible evaluated value of the formula after inserting an arbitrary number of pairs of parentheses.

Constraints

1≦N≦10^5

1≦A_i≦10^9

op_i is either + or -.

Input

The input is given from Standard Input in the following format:

N
A_1 op_1 A_2 ... op_{N-1} A_N

Output

Print the maximum possible evaluated value of the formula after inserting an arbitrary number of pairs of parentheses.

Sample Input 1

3
5 - 1 - 3

Sample Output 1

7

The maximum possible value is: 5 - (1 - 3) = 7.

Sample Input 2

5
1 - 2 + 3 - 4 + 5

Sample Output 2

5

The maximum possible value is: 1 - (2 + 3 - 4) + 5 = 5.

Sample Input 3

5
1 - 20 - 13 + 14 - 5

Sample Output 3

13

The maximum possible value is: 1 - (20 - (13 + 14) - 5) = 13.

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

// package atcoder.arc.arc066;

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.InputMismatchException;

public class Main {
    static final long INF = (long)1e18;

    public static void main(String[] args) {
        InputReader in = new InputReader(System.in);
        PrintWriter out = new PrintWriter(System.out);

        int n = in.nextInt();

        int[] flg = new int[n];
        long[] num = new long[n];
        for (int i = 0; i < n ; i++) {
            num[i] = in.nextInt();
            if (i+1 < n) {
                flg[i+1] = in.nextToken().toCharArray()[0] == '+' ? 1 : -1;
            }
        }
        flg[0] = 1;
        
        long[][] dp = new long[n+1][3];
        for (int i = 0; i <= n; i++) {
            Arrays.fill(dp[i], -INF);
        }
        dp[0][0] = 0;
        for (int i = 0; i < n ; i++) {
            for (int c = 0; c <= 2; c++) {
                long base = dp[i][c];
                if (base == -INF) {
                    continue;
                }
                long add = ((c % 2 == 0) ? 1 : -1) * flg[i] * num[i];

                if (flg[i] == -1) {
                    for (int tc = c ; tc <= Math.min(2, c+1) ; tc++) {
                        dp[i+1][tc] = Math.max(dp[i+1][tc], base+add);
                    }
                }
                for (int tc = c ; tc >= 0 ; tc--) {
                    dp[i+1][tc] = Math.max(dp[i+1][tc], base+add);
                }
            }
        }
        out.println(dp[n][0]);
        out.flush();
    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        private int[] nextInts(int n) {
            int[] ret = new int[n];
            for (int i = 0; i < n; i++) {
                ret[i] = nextInt();
            }
            return ret;
        }

        private int[][] nextIntTable(int n, int m) {
            int[][] ret = new int[n][m];
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    ret[i][j] = nextInt();
                }
            }
            return ret;
        }

        private long[] nextLongs(int n) {
            long[] ret = new long[n];
            for (int i = 0; i < n; i++) {
                ret[i] = nextLong();
            }
            return ret;
        }

        private long[][] nextLongTable(int n, int m) {
            long[][] ret = new long[n][m];
            for (int i = 0; i < n; i++) {
                for (int j = 0; j < m; j++) {
                    ret[i][j] = nextLong();
                }
            }
            return ret;
        }

        private double[] nextDoubles(int n) {
            double[] ret = new double[n];
            for (int i = 0; i < n; i++) {
                ret[i] = nextDouble();
            }
            return ret;
        }

        private int next() {
            if (numChars == -1)
                throw new InputMismatchException();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public char nextChar() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            if ('a' <= c && c <= 'z') {
                return (char) c;
            }
            if ('A' <= c && c <= 'Z') {
                return (char) c;
            }
            throw new InputMismatchException();
        }

        public String nextToken() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            StringBuilder res = new StringBuilder();
            do {
                res.append((char) c);
                c = next();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public int nextInt() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = next();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c-'0';
                c = next();
            } while (!isSpaceChar(c));
            return res*sgn;
        }

        public long nextLong() {
            int c = next();
            while (isSpaceChar(c))
                c = next();
            long sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = next();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c-'0';
                c = next();
            } while (!isSpaceChar(c));
            return res*sgn;
        }

        public double nextDouble() {
            return Double.valueOf(nextToken());
        }

        public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

    static void debug(Object... o) {
        System.err.println(Arrays.deepToString(o));
    }
}