#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

int main()
{
    int p;
    fin >> p;
    int n;
    if(p == 0)
    {
        n = 1;
    }
    else
    {
        int zerouri = 0, k = 1, i = 1,limita = 5;
        while(zerouri < p)
        {
            zerouri += k;
            if(i == limita)
            {
                limita *= 5;
                k++;
            }
            i++;
        }
        if(zerouri == p)
        {
            n = 5 * (i - 1);
        }
        else
        {
            n = -1;
        }
    }
    fout << n;
    fin.close();
    fout.close();
    return 0;
}