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::{BufRead, Write};
use std::io;
use std::ops::{Add, Sub};

fn solve<R: BufRead, W: Write>(mut input: R, mut output: W) {
    let mut buf = String::new();
    input.read_line(&mut buf).unwrap();
    let (a, b, c, d): (i8, i8, i8, i8) = {
        (buf[0..1].parse().unwrap(), buf[1..2].parse().unwrap(), buf[2..3].parse().unwrap(), buf[3..4].parse().unwrap())
    };
    let ops: [(fn(i8, i8) -> i8, char); 2] = [(i8::add, '+'), (i8::sub, '-')];
    'outer: for (i_op, i_chr) in ops.iter().cloned() {
        for (j_op, j_chr) in ops.iter().cloned() {
            for (k_op, k_chr) in ops.iter().cloned() {
                if (k_op(j_op(i_op(a, b), c), d)) == 7 {
                    writeln!(output, "{}{}{}{}{}{}{}=7", a, i_chr, b, j_chr, c, k_chr, d).unwrap();
                    break 'outer;
                }
            }
        }
    }
}

fn main() {
    let stdin = io::stdin();
    let stdout = io::stdout();
    solve(stdin.lock(), stdout.lock());
}

#[cfg(test)]
mod tests {
    fn test(input: &str, output: &str) {
        let mut v: Vec<u8> = Vec::new();
        ::solve(input.as_bytes(), &mut v);
        assert_eq!(String::from_utf8(v).unwrap(), output);
    }

    #[test]
    fn case1() {
        test(
            "1222
",
            "1+2+2+2=7
",
        );
    }

    #[test]
    fn case2() {
        test(
            "0290
",
            "0-2+9+0=7
",
        );
    }

    #[test]
    fn case3() {
        test(
            "3242
",
            "3+2+4-2=7
",
        );
    }
}