#include <fstream>

using namespace std;
ifstream cin ("fact.in");
ofstream cout ("fact.out");
int zero(int n)
{
    int p=5,sum=0;
    while (p<=n)
    {
        sum=sum+n/p;
        p=p*5;
    }
    return sum;
}
long long p,l,r,m,sol=-1;
int main()
{
    cin >>p;
    if (p==0)
    {
        cout <<1;
    }
    else
    {
        l=0;
        r=500000000;
        while (l<=r)
        {
            m=(l+r)/2;
            if (zero(m)<p)
            {
                l=m+1;
            }
            else if (zero(m)==p)
            {
                sol=m;
                r=m-1;
            }
            else
            {
                r=m-1;
            }
        }
        cout <<sol;
    }
    return 0;
}