#include <fstream>

using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");

int st=1,dr=1000005,p,mij,nr=-1,nrr;

int zero(int n)
{
    int aux,aux2;
    for ( aux=5; aux<=n; aux*=5)
        aux2+=(n/aux);
    return aux2;
}

int program()
{
    if ( p==0)
        return 1;
    while( st<=dr)
    {

        int mij=(dr-st)/2+st;
        if ( zero(mij)==p)
        {
            nr=mij;
            dr=mij-1;
        }
        else if ( zero(mij)>p)
            dr=mij-1;
        else
            st=mij+1;
    }
}

int main()
{
    in>>p;
    nrr=program();
    out<<nrr<<'\n';
    return 0;
}