#include <fstream>
#include <climits>

using namespace std;
int zero(int n)
{
 if(n==0) return 0;
 return n/5+zero(n/5);
}


int main()
{
    ifstream f("fact.in");
    ofstream g("fact.out");

   int p,n=INT_MAX,i,y,x,xx;
    i=1; y=n;
    bool ok=0;
    f>>p;
    while(i<=y)
        {
            x=(i+y)/2;
            if(zero(x)==p)
                {
                    ok=1;
                    for(xx=x; xx>=1; xx--)
                        if(zero(xx)!=p)
                            break;
                    g<<xx+1;
                    break;
                }
            else
                if(p>zero(x))
                    i=x+1;
                else
                    y=x-1;

        }

    if (ok==0)
        g<<-1;




}