#include<stdio.h>
#include<math.h>

void main()
{
 long p;
 FILE *f,*g;
 f=fopen("fact.in","r");
 g=fopen("fact.out","w");
 fscanf(f,"%ld",&p);
 if(p==0)
	 fprintf(g,"%d",1);
 else{
	long k=0;
	long i=1;
	while(pow(5,i+1)<5*p){
		if(k!=0){
		k=k+3;
		}
		if(2*pow(5,i+1)<5*p) k++;
		if(3*pow(5,i+1)<5*p) k++;
		if(4*pow(5,i+1)<5*p) k++;
		k=k+i;
		i++;
		}
 fprintf(g,"%ld",5*(p-k));
	 }



   fclose(f);
 fclose(g);

}