#include<fstream>
#include<cmath>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
unsigned long long int cautare(unsigned long long int val);
unsigned long long int a[1000001],p,k=25,nr=0,i,x;
int main()
{


    fin>>p;
    a[1]=1;
    for(i=2;i<=900001;i++)
    {
        if(i*5!=k)
        {
            a[i]=a[i-1]+1;
        }
        else
        {
            a[i]=a[i-1]+2;
            k=k*5;
        }
    }


    x=cautare(p)-1;
    if(a[x]==p)
    {

        fout<<x*5;
    }
    else
    {
        fout<<-1;
    }

}
unsigned long long int cautare(unsigned long long int val)
{
    unsigned long long int st=1,dr=900001,mij;
    while(st<=dr)
    {
        mij=(st+dr)/2;
        if(a[mij]>val)
            dr=mij-1;
        else
            st=mij+1;
    }
    return st;
}