#include<stdio.h>
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	long p,i,j,s,m;
	scanf("%ld",&p);
	i=0;
	j=1;
	s=0;
	if(p==0)
		printf("1");
	else
	{
	 i=p*5;
	 for(j=5;j<=i;j=j+5)
	 {
		 m=j;
		 m=m/5;
		 while(m%5==0)
		 {
			 i=i-5;
			 m=m/5;
		 }
	 }
	printf("%ld",i);
	}
	return 0;
}