#include <iostream>
#include <fstream>

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

int zero(int n)
{
    int p5 = 0, ci;
    for(int i = 1; i <= n; i++)
    {
        ci = i;
        while(ci%5 == 0)
        {
            p5 = p5+1;
            ci = ci/5;
        }
    }
    return p5;
}

int main()
{
    int p, n, p5, ci;

    fin>>p;
    n = 0;
    while(p5 != p)
    {
        p5 = zero(n);
        n = n + 1;
        if(p5>p)
        {
            break;
        }
    }
    if(p5 == p)
    {
        fout<<n-1<<endl;
    }
    else
    {
        fout<<-1<<endl;
    }


}