#include <iostream>
#include <cstring>
#include <stdlib.h>
using namespace std;

int main() {
    long long m=0;
    long long n;
    char num[50];
    std::cin.getline(num, 50);
    string number(num);
    for (int i = 0; i<number.length(); i++) {
        if (number[i]==' ') {
            number.erase(i,1);
        }
    }
    n = atoi(number.c_str());
    if(n==1) {
        cout << "1";
    } else {
        if(n<10) {
            cout << "1" << n << "\n";
        } else {
            for(int i=9;i>1;i--)
            {
                if(n%i==0)
                {
                    n=n/i;
                    m=m*10+i;
                    i++;
                }
            }
            if(n!=1) {
                cout << "-1" << "\n";
            } else {
                char buf[50];
                sprintf(buf, "%Ld", m);
                string s(buf);
                for (int j = s.length()-1; j>=0; j--) {
                    cout << s[j];
                }
            }
        }
    }
}
This is solution. What wrong with test 8? For number 1 000 000 000 result is 555555555888

Try these tests:
0 -> 10
12 -> 26
112 -> 278

all this tests ok

But you have already got AC in this problem. Why do you care about it now? :)