#include<stdio.h>
FILE *in=fopen("fact.in","rt");
FILE *out=fopen("fact.out","wt");
long int zero(long int n,long int f)
{
 long int total,nr;
 if(n==5) return 1;
 total=0;
 nr=f;
 while(nr<n)
 {
	total=total+n/nr;
	nr=nr*f;
 }
 return total;
}
int main()
{
 long int n,p,ok;
 fscanf(in,"%ld",&p);
 if(p==0) fprintf(out,"0");
 else
 {
	 ok=0;n=0;
	 while(!ok)
	 {
		n++;
		if(p==zero(n,5)) ok=1;
	 }
	 fprintf(out,"%ld",n);
 }
 return 0;
}