#include<iostream>

 #include<cstring>

 #include<cstdio>

 #include<cmath>

 #include<algorithm>

 #include<cstdlib>

 using namespace std;

 char s[];

 int main(){

     cin>>s;

     int len=strlen(s);

     int num1=,num2=;

     for(int i=;i<len;i++){

         if(s[i]=='')num1++;

         if(s[i]=='')num2++;

     }

     if(num1>=num2&&num1!=)cout<<""<<endl;

     else if(num1<num2)cout<<""<<endl;

     else cout<<"-1"<<endl;

 }