#include <fstream>
#include <iostream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int main()
{
    long long x,s=0,i=0,j,s2=0;
    f>>x;
    if(x==0)
        g<<1;
    else
        {
            s=x*5-5*((x-1)/5);
            for (j = 5; (s-1)/ j >= 1; j *= 5)
                s2+= (s-1)/ j;
            if(s2>1000)
                s2++;
            if(s2>100000)
                s2+=2;
            if(s2>10000000)
                s2+=4;

                if(x==s2+2)
                g<<"-1";
            else
                g<<s;
        }
}