#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
int sol1(int x)
{
    int sol,rez=0,cont=0;
    while(x>rez)
    {
        cont++;
        sol=(x/5)*4+cont;
        rez=sol;
        while(sol/5)
        {
            rez+=sol/5;
            sol/=5;
        }
    }
    if(x==rez)
        if(x==0)
            sol=1;
        else
            sol=((x/5)*4+cont)*5;
    else
        sol=-1;
    return sol;
}
int main()
{
    int x;
    f>>x;
    g<<sol1(x);
}