#include <fstream>
#include <string.h>

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=1;i<lung;i++){
            if(s[i]>=65&&s[i]<=122)
                litere++;
            else
            if((s[i]==' '&&litere!=0)||(s[i]=='-'&&litere!=0))
                cuvinte++;
    }
    if(s[0]>=65&&s[0]<=122){
        cuvinte++;
        litere++;
    }
    ofstream out ("text.out");
    if(cuvinte==0)
        out<<-1;
    else
    out<<litere/cuvinte;
    out.close();
    return 0;
}