#include<fstream>
using namespace std;
int st,dr,p,nr;
int f(int n)
{
    int s,x;
    x=n;
    s=0;
    while(x!=0)
    {
        x=x/5;
        s=s+x;
    }
    return s;
}
int main()
{
     ifstream fin("fact.in");
    ofstream fout("fact.out");
    fin>>p;
    st=1;
    dr=5*p;
    while(st<=dr)
    {
        nr=st+(dr-st)/2;
        if(f(nr)<p)
        {
            st=nr+1;
        }
        if(f(nr)>p)
        {
            dr=nr-1;
        }
        if(f(nr-1)<p && f(nr+1)>p)
        {
            dr=-2;
            break;
        }
    }
    fout<<dr+1;
    fin.close();
    fout.close();
    return 0;
}