#include<stdio.h>
//#include<conio.h>
inline unsigned long long getfive(unsigned long long x)
{
	unsigned long n=0;
   while(x%5==0)
   {
   	n++;
      x/=5;
   }
   return n;
}
int main()
{
	unsigned long long nr,x,j,in=0,out=0,i;
   FILE *fi,*fo;
   fi=fopen("fact.in","r");
   fo=fopen("fact.out","w");
   fscanf(fi,"%llu",&nr);
   nr*=5;
   for(i=25;i<=nr;i+=25)
   {
		in+=getfive(i)-1;
      //printf("testam pt i=%lu; acesta aduce %lu 5-uri. in devine %lu\n",i,getfive(i)-1,in);getch();
      while(out<in)
      {
      	//printf("scoatem %lu. pierdem 1 5-uri(out:%lu). nr devine %lu\n",nr,out+1,nr-5);getch();
      	out++;
         nr-=5;
      }
   }
   //printf("terminat. nr este %lu; in:%lu out:%lu",nr,in,out);getch();
   fprintf(fo,"%llu",nr);
   return 0;
}