#include <stdio.h>
long P;

int main()
{
	freopen ("fact.in","r",stdin);  
	freopen ("fact.out","w",stdout);
	scanf("%ld",&P);  
	long BigGuess = 1;

	if (BigGuess == 0)
	{
		printf("%ld\n",1);
		return 0;
	}
	else
	{
		BigGuess = P*5;

		long i = 25 ;
		long SmallGuess = BigGuess;
		while ( i < BigGuess )
		{
			i = i * 5;
			SmallGuess = SmallGuess - 5;
		}

		printf("%ld\n",SmallGuess);
	}
	return 0;
}