#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int nr0(int x)
{
    int s = 0;
    int p = 5;
    while(p <= x)
    {
        s += x / p;
        p *= 5;
    }
    return s;
}
int main()
{
    int p,nr;
    bool ok = false;
    fin>>p;
    if(p==0){
        fout<<1;
        return 0;
    }
    int st = 2, dr = 500000000, m;
    while(st <= dr)
    {
        m = (st + dr) / 2;
        nr = nr0(m);
        if(nr==p){
            ok=true;
            m -= m % 5;
            break;
        }
        if(nr > p)
            dr = m - 1;
        else
            st = m + 1;
    }
    if(ok)
        fout << m;
    else
        fout <<- 1;
    return 0;
}