#include<stdio.h>
long n;
long factorial(long n)
{
		long num=0,nr=0;
		num=5;
		while(n/num)
			{
				nr=nr+n/num;
				num=num*5;
			}
		return nr;
}



long bs(long val)
{
		long st=1,dr=10,med,last;
		while(st<=dr)
			{
				med=st+(dr-st)/2;
				if(factorial(med)>=val)
					{
						last=med;
						dr=med-1;
					}
				else
					st=med+1;
			}
		return last;
}




int main()
{	
		freopen("fact.in","r",stdin);
		freopen("fact.out","w",stdout);
		scanf("%ld",&n);
		printf("%ld\n",bs(n));
		return 0;	
}