#include <iostream>
#include <string>
using namespace std;

int main() {
	std::string turnsDefined;
	std::cin >> turnsDefined;
	bool hasPassed = false;    
	while(hasPassed != true){
	    for(char c : turnsDefined){
	        if(isdigit(c) != true){
	            std::cout << "Please only use numbers to describe the amount of turns you'd like to do." << std::endl;
	            hasPassed = false;
	            break;
	            std::cin >> turnsDefined;
	        }else{
	            hasPassed = true;
	        }
	    }
	}
	return 0;
}