#include <iostream>
#include <fstream>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
void fact(int n)
{
    if(n==0)out<<1;
    else if(n<0)
        out<<-1;
    else
    {
        int i,k,c=0;
        for(k=0;k<n;k++)
            c=c+5;
        out<<c;
    }
}
int main()
{
    int n;
    in>>n;
    in.close();
    fact(n);
    return 0;
}