//#include<iostream>
#include<fstream>
using namespace std;
unsigned long long int v[14];
int main ()
{
    unsigned int i=1, p, nr =0;
    ifstream g ("fact.in");
    ofstream h ("fact.out");
    g>>p;
    while (nr<p)
    {
        v[i]++; nr++;
        if(v[i]%5==0)
        i++;
        else
            if(i>1)
                i=1;
    }
    /*i=1;
    while(v[i]>0)
    {
        cout<<v[i]<<" ";
        i++;
    }*/
    //cout<<i-1;
    if(v[1]==0)
        h<<"-1";
    else
        h<<v[1]*5;
    g.close();
    h.close();
    return 0;
}