Problem:
Score : 300 points

Problem Statement

Sitting in a station waiting room, Joisino is gazing at her train ticket.

The ticket is numbered with four digits A, B, C and D in this order, each between 0 and 9 (inclusive).

In the formula A op1 B op2 C op3 D = 7, replace each of the symbols op1, op2 and op3 with + or - so that the formula holds.

The given input guarantees that there is a solution. If there are multiple solutions, any of them will be accepted.

Constraints

0≤A,B,C,D≤9

All input values are integers.

It is guaranteed that there is a solution.

Input

Input is given from Standard Input in the following format:

ABCD

Output

Print the formula you made, including the part =7.

Use the signs + and -.

Do not print a space between a digit and a sign.

Sample Input 1

1222

Sample Output 1

1+2+2+2=7

This is the only valid solution.

Sample Input 2

0290

Sample Output 2

0-2+9+0=7

0 - 2 + 9 - 0 = 7 is also a valid solution.

Sample Input 3

3242

Sample Output 3

3+2+4-2=7

Solution in Rust (1.15.1) (judge verdict: Accepted)

use std::io::{stdin, Read};
use std::str::FromStr;

// https://qiita.com/tubo28/items/e6076e9040da57368845
fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("failed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

/*
#[allow(dead_code)]
fn main() {}
*/
#[allow(dead_code)]
fn main() {
    fn make_set(n: usize) -> Vec<Vec<usize>> {
        let width = 1 << n;
        let mut result_set = vec![];
        for bits in 0..width {
            let mut row = vec![];
            for i in 0..n {
                if bits >> i & 1 == 1 {
                    row.push(i)
                }
            }
            result_set.push(row)
        }
        result_set
    }

    let s = read::<String>();
    let s = s
        .chars()
        .into_iter()
        .map(|c| c.to_digit(10).unwrap())
        .map(|x| x as i32)
        .collect::<Vec<_>>();

    let op_pos = make_set(s.len() - 1);

    for pos in op_pos {
        let mut op = vec![-1 as i32; 4];
        for p in pos {
            op[p] = 1;
        }

        if s[0] + s[1] * op[0] + s[2] * op[1] + s[3] * op[2] == 7 {
            let os = op
                .into_iter()
                .map(|c| if c < 0 { "-" } else { "+" })
                .collect::<Vec<_>>();
            println!(
                "{}{}{}{}{}{}{}=7",
                s[0], os[0], s[1], os[1], s[2], os[2], s[3]
            );
            use std::process::exit;
            exit(0)
        }
    }
}