#include <fstream>

using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");

int nr_zero(int n)
{
    int nr=0;
    while(n>=5)
    {
        nr+=n/5;
        n/=5;
    }
    return nr;
}
int caut_n(int p)
{
    int st=0,dr=500000000,rez=dr+1;
    while(st<=dr)
    {
        int m=(st+dr)/2;
        if(nr_zero(m)>=p)
        {
            rez=m;
            dr=m-1;
        }
        else
            st=m+1;
    }
    return rez;
}
int main()
{
    int p,r;
    in>>p;
    r=caut_n(p);
    if(r==500000000)
        out<<-1;
    else
        out<<r;
    return 0;
}