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::*;
use std::str::FromStr;
use std::collections::HashMap;
use std::collections::BTreeSet;
use std::collections::HashSet;
use std::cmp;
use std::f64::consts;

fn main() {
    let input: String = read();
    let vec: Vec<char> = input.chars().collect();
    let mut vec_i: Vec<i32> = Vec::new();

    for &c in vec.iter() {
        let i: i32 = c.to_digit(10).unwrap() as i32;
        vec_i.push(i);
    }

    for i in 0..i32::pow(2, vec.len() as u32 -1) {
        let mut s = vec[0].to_string();
        let mut sum = vec_i[0];
        for j in 0..vec.len()-1 {
            if (1 & i >> j) == 1 {
                sum += vec_i[j+1];
                s = format!("{}+{}", s, vec[j+1]);
            } else {
                sum -= vec_i[j+1];
                s = format!("{}-{}", s, vec[j+1]);
            }
        }

        if sum == 7 {
            s = format!("{}=7", s);
            println!("{}", s);
            break;
        }
    }
}

fn calc_distance(x: i32, y: i32, target_x: i32, target_y: i32) -> i32 {
    let diff_x = (target_x - x).abs();
    let diff_y = (target_y - y).abs();

    return diff_x + diff_y;
}

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")
}

// 最大公約数
fn gcd(a: i32, b: i32) -> i32 {
    match b {
        0 => a,
        _ => gcd(b, a % b)
    }
}

// 最小公倍数
fn lcm(a: i32, b: i32) -> i32 {
    a * b / gcd(a, b)
}

// 階乗
fn kaijou(n: i32)->i32 {
    if n == 1 {
        return n;
    }
    return n * kaijou(n-1);
}