#include <fstream>

using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
int p2,mij,div5,i,p;
int p1=1,n;
int main()
{
            p2=2147483646;
            fin>>n;
if(n==0)fout<<1;
else{

    while(p1<p2)
    {  mij=(p1+p2)/ 2;
    div5=mij/5;
              if(div5<=n) for(i=25;i<=mij;i=i*5)
                {
                    p++;
                    div5=div5+p;
                }
                p=0;
                if(div5>n)p2=mij-1;
                else
                {
                            if(div5<n)p1=mij+1;
                            else break;
                }
    }
    if(div5==n)fout<<mij-mij%5;
    else fout<<-1;
        }
        fin.close();
        fout.close();
    return 0;
}