#include <fstream>
using namespace std;
ifstream f("fact.in");
ofstream g("fact.out");
long long nrz,n,m,nrz1;
int main()
{
f>>nrz;
n=nrz*4;
while(nrz1<nrz)
{
    //g<<n<<" ";
    nrz1=0;
    m=n;
    while(m!=0)
    {
        m=m/5;
        nrz1=nrz1+m;
    }
    //g<<nrz1<<"\n";
    n++;
}
if(nrz1!=nrz)
{
    g<<-1;
}
else
{
    if(nrz==0)
    {
        g<<1;
    }
     else
    {
        g<<n-1;
    }
}
return 0;
}