pod.cpp

#include <iostream>
#include <iterator>
#include <algorithm>
#include <string>

using namespace std;

int main(){

	for(
	std::istream_iterator<int> iiter(std::cin), eof;
	 ++iiter != eof;){

		int n = *iiter;
		
		if( n < 10 ){
			cout << n << endl;	
		}	

		else {
		
			std::string result;		
			for(int i = 10 ; --i > 1 ; )
				
				for( ;
					n % i == 0 ;
					n /= i,
				   	result = ::to_string(i) + result
				);

			cout << (n ^ 1 ? -1 : ::stoi(result)) << endl;
		}
	}
}

uva product of digits