#include <fstream>
#include <iostream>
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");
long long p,n,pas,elem,k,j;
int main()
{fin>>p;
 pas=1;
 elem=5;
 while(k==0)
      {if(p<=pas*5+1) k=1;
         else {pas=pas*5+1;elem=elem*5;}
      }
 while(p>0)
      {for(j=1;j<=5;j++)
          {
          if(((j-1)*pas<=p)&&(p<=j*pas)){if(pas>=5){n=n+elem*(j-1);p=p-pas*(j-1);pas=(pas-1)/5;elem=elem/5;j=0;if(p==0)break;}
                                         else {n=n+elem*j;
                                               p=p-pas*j;
                                               pas=(pas-1)/5;
                                               elem=elem/5;
                                               if(p<=0) break;}
                                        }
          }
      }
 fout<<n;
}