#include <fstream>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

int main()
{
    int n=0,p,k=0,cop,i;
    f>>p;
    if(p==0)
        g<<-1;
    else
    {
        for(i=5; k<p; i++)
        {
            cop=i;
            while(cop%5==0)
            {
                cop=cop/5;
                k++;
            }
            if(i%5==0)
                n=n+5;
        }
        g<<n;
    }
    return 0;
}