#include <stdio.h>

int n;

long long cautare_binara(long long li,long long ls)

 {
  long long m,p,i;
  if (li<=ls) {
                  m=(li+ls)/2;
                  p=m;i=0;
                  while (p>0)
                    {p=p/5;
                     i=i+p;
                    }
                  if (i==n) return m;
                       else if (i>n) return cautare_binara(li,m-1);
                                else return cautare_binara(m+1,ls);
                 }
          else return -1;
 }



int main()
{FILE *fin,*fout;

 fin=fopen("fact.in","r");
 fscanf(fin,"%d",&n);
 fclose(fin);

 fout=fopen("fact.out","w");
 if (n==0) fprintf(fout,"%d",1);
      else fprintf(fout,"%lld",cautare_binara(1,3000000000));
 fclose(fout);

return 0;
}