#include<stdio.h>
int main()
{
   unsigned long put5[]={25,125,625,3125,15625,78125,390625,1953125,9765625,48828125,244140625,1220703125};
	unsigned long nr,scad,j;
   int i;
   FILE *fi,*fo;
   fi=fopen("fact.in","r");
   fo=fopen("fact.out","w");
   fscanf(fi,"%lu",&nr);
   nr*=5;
   for(i=0;i<=11;i++)
      if(put5[i]<=nr)
   		{
            scad=(int)nr/put5[i];
            for(j=1;j<=scad;j++)
            {
               if(nr%put5[i]==0){scad--;if(j>scad)break;}
               nr-=5;
            }
         }
   fprintf(fo,"%lu",nr);
   return 0;
}