#include <fstream>
#include <climits>
using namespace std;
int zero(int n)
{
    int x;
    int k=0,y;
    for(x=5;x<=n;x=x++)
    {
        y=x;
        while(y%5==0)
        {
            k++;
            y=y/5;
        }
    }
    return k;
}
int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");
    int N,P,ok,p,q,m;
    f>>P;
    N=1;
    ok=0;
    p=N;
    q=INT_MAX;
    while(p<=q)
    {
        N=(p+q)/2;
        if(zero(N)==P)
        {
            ok=1;g<<N;break;
        }
        else
        {
            if(P>zero(N))
            {
                p=N+1;
            }
            else
            {
                q=N-1;
            }
        }
    }
    if(ok==0)
    g<<-1;
    return 0;
}