#include <fstream>
#include <string.h>
#include <iostream>
using namespace std;

char s[999999999];

int main(){
    ifstream in ("text.in");
    in.getline(s,999999999);
    in.close();
    int i,lung,cuvinte,litere;
    cuvinte=0;
    litere=0;
    lung=strlen(s);
    for(i=0;i<lung;i++){
            if((s[i]>='a'&&s[i]<='z')||(s[i]>='A'&&s[i]<='Z'))
                litere++;
            else
                if((s[i]==' ')||(s[i]=='-'&&litere!=0))
                    cuvinte++;
    }
    ofstream out ("text.out");
    if(cuvinte==0)
        out<<-1;
    else
    out<<litere/cuvinte;
    out.close();
    return 0;
}