#include <iostream>

using namespace std;

bool isNumber(string s) {
    if(s.size()==0) return false;
    for(int i=0;i<s.size();i++) {
    	if((s[i]>='0' && s[i]<='9')==false) {
            return false;
        }
    }
    return true;
}

int main()
{
   if(isNumber("1243")) {
       cout << "It is a number!";
   }
   else {
       cout << "It is not a number!";
   }
   return 0;
}