#include <fstream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p,m,s,n;
int main()
{
    fin>>p;
    n=4*p;
    while(s<p)
    {
        s=0;m=n;
        while(m!=0)
        {
            m/=5;
            s+=m;
        }
        n++;
    }
    if(s!=p)
        fout<<-1;
    else if(p==0)
        fout<<1;
    else
        fout<<n-1;
    return 0;
}