#include <iostream>
#include <fstream>
using namespace std;

int main()
{ifstream fin ("fact.in");
ofstream fout ("fact.out");
int P,a,b,j,i;
fin>>P;
a=5*P;
b=P;
if (P==0)
  fout<< 1;
else
  {for (i=5;i<=b;i+=5)
      {j=i;
       while (j%5==0)
          {j=j/5;
           a-=5;
           b--;
      }
      }
  fout<<a;
  }
fin.close();
fout.close();
return 0;
}