#include<iostream>
#include<string>
using namespace std;
int main()
{
    string s,cleaned="";
    getline(cin,s);
    
    for(int i = 0;i<s.length();i++){
        if(s[i]=='-'){
            cout<<"invalid input";
            return 0;
        }
        if((s[i]>='a'&&s[i]<='z')||(s[i]>='a'&&s[i]<='z')||(s[i]>='0'&&s[i]<='9')||s[i]==''){
            cleaned+=s[i];
        }
    }
    cout<<cleaned;
    return 0;
}