#include<fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long x,m;
int verif(long long k)
{
    int nr=0;
    while(k)
    {
        nr=nr+k/5;
        k=k/5;
    }
    return nr;
}
void cautbin(long long st,long long dr,long long x)
{
    long ok=0;
    while(st<=dr&&!ok)
    {
        m=(st+dr)/2;
        if(verif(m)==x)
            ok=1;
        else
            if(x>verif(m))
                st=m+1;
            else
                dr=m-1;
    }
    if(ok==0)
        m=-1;
}
   int main()
{
    f>>x;
    cautbin(1,999999999,x);
    if(m!=-1)
    {
        while(m)
        {
            if(verif(m)==x)
                m--;
            else
                break;
        }
        g<<m+1;
   }
    else
        g<<m;
    return 0;
}