#include <iostream>
#include <fstream>
#define NMax 100000001
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int fct (int x)
{
    int a=5,rez=0;
    while (x/a)
    {
        rez=rez+x/a;
        a=a*5;
    }
    return rez;
}
int main ()
{
    int p,val;
    f>>p;
    if (p==0) g<<1;
    else
    {
        int min=1,max=NMax,mid;
        bool ok=false;
        while (min<max && !ok)
        {
            mid=(min+max)/2;
            val=fct(mid);
            if (val<p) min=mid+1;
            else if (val>p) max=mid-1;
            else ok=true;
        }
        if (ok)
        {
            while (mid%5) mid--;
            g<<mid;
        }
        else g<<-1;
    }
}