Problem:
Score : 400 points

Problem Statement

Find the largest integer that can be formed with exactly N matchsticks, under the following conditions:

Every digit in the integer must be one of the digits A_1, A_2, ..., A_M (1 \leq A_i \leq 9).

The number of matchsticks used to form digits 1, 2, 3, 4, 5, 6, 7, 8, 9 should be 2, 5, 5, 4, 5, 6, 3, 7, 6, respectively.

Constraints

All values in input are integers.

2 \leq N \leq 10^4

1 \leq M \leq 9

1 \leq A_i \leq 9

A_i are all different.

There exists an integer that can be formed by exactly N matchsticks under the conditions.

Input

Input is given from Standard Input in the following format:

N M
A_1 A_2 ... A_M

Output

Print the largest integer that can be formed with exactly N matchsticks under the conditions in the problem statement.

Sample Input 1

20 4
3 7 8 4

Sample Output 1

777773

The integer 777773 can be formed with 3 + 3 + 3 + 3 + 3 + 5 = 20 matchsticks, and this is the largest integer that can be formed by 20 matchsticks under the conditions.

Sample Input 2

101 9
9 8 7 6 5 4 3 2 1

Sample Output 2

71111111111111111111111111111111111111111111111111

The output may not fit into a 64-bit integer type.

Sample Input 3

15 3
5 4 6

Sample Output 3

654

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

use std::io::prelude::*;

fn input<T>() -> T
    where T: std::str::FromStr {
    let stdin = std::io::stdin();
    let token: String = stdin
        .lock()
        .bytes()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().unwrap()
}

fn main() {
    let mut n = input::<usize>();
    let m = input::<usize>();
    let aa = (0..m).map(|_| input::<usize>()).collect::<Vec<_>>();
    let nums = [
        0, 2, 5, 5, 4, 5, 6, 3, 7, 6
    ];
    let mut usable = vec![false; 10];
    for a in aa { usable[a] = true; }
    let mut dp = vec![None; n+1];
    dp[0] = Some(0);
    for i in 0..n+1 {
        for j in 1..10 {
            if !usable[j] { continue; }
            if i >= nums[j] {
                dp[i] = std::cmp::max(dp[i], dp[i-nums[j]].map(|v| v+1));
            }
        }
    }
    let mut ans = vec![];
    while n > 0 {
        for j in (1..10).rev() {
            if !usable[j] { continue; }
            if n >= nums[j] && dp[n-nums[j]] == dp[n].map(|v| v-1) {
                n-=nums[j];
                ans.push(j);
                break;
            }
        }
    }
    println!("{}", ans.iter().map(|v| v.to_string()).collect::<String>());

}