#include<fstream>

using namespace std;

FILE*in;
ofstream out("fact.out");

long nr_zero_sought;
long nr_zero_calculated;
long long number;
long long mirror;

void read()
{
    in=fopen("fact.in", "r");

    fscanf(in, "%ld", &nr_zero_sought);
}

void solve()
{
    number=4*nr_zero_sought;

    while (nr_zero_calculated < nr_zero_sought)
    {
        nr_zero_calculated=0;
        mirror=number;

        while (mirror)
        {
            mirror/=5;
            nr_zero_calculated+=mirror;
        }

        number++;
    }
}

void show()
{
    if (nr_zero_sought == 0)
        out<<1;
    else if (nr_zero_calculated < nr_zero_sought)
        out<<-1;
    else
        out<<number-1;
}

int main()
{
    read();
    solve();
    show();

    return 0;
}