#include<fstream>
using namespace std;
ifstream f("factorial.in");
ofstream g("factorial.out");
int nrz(int x)
{
int rez=0,p=5;
  while(p<x)
    {
        rez+=x/p;
        p*=5;
    }
    if(!rez)
    return 1;
    else
    return rez;
}

long long cautbin(long long n)
{long long mij=0;
    long long st=0;
   long long dr=100000000;
    while(st<dr)
      {
          mij=(st+dr)/2;
          if(nrz(mij)>n)
          dr=mij;
          else
          st=mij+1;
      }
   return st;
}
int main()
{int n;
f>>n;
if(n==0)
   g<<1;
   else
   if(nrz(cautbin(n)-5)!=n)
   g<<-1;
   else
 g<<cautbin(n)-5;
 return 0;
}