#include <iostream>
#include <fstream>

using namespace std;


int hany5(int num)
{
    int ret = 0;

    while(num % 5 == 0)
    {
        num /= 5;
        ret++;
    }

    return ret;
}

int solve_me(unsigned long int p)
{
    int i = 1;
    int total = 0;

    while(total < p)
    {
        total += hany5(i);
        i++;
    }


    if(total == p)
        return i-1;
    else
        return -1;
}

int main()
{
    ifstream in("factorial.in");
    ofstream out("factorial.out");

    int P; in >> P; in.close();

    out << solve_me(P);

    out.close();

    return 0;
}