#include <iostream>
#include <fstream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");
int verif(int x)
{
    int i=1;
    int sum=5;
    while(sum<x)
    {
        sum*=5;
        i++;
    }
    if(x==sum)
        return i;
    return 1;
}

int main()
{
    int p,i;
    in>>p;
    if(p==0)
    {
        out<<1;
        return 0;
    }
    int z=0;

    for(i=5;z<p;i=i+5)
    {
        z=z+verif(i);

    }
    if(z==p)
        out<<i-5;
    else
        out<<-1;

}