#include<stdio.h>
int zero(int n)
{
	int nr=0;
	while(n)
	{
		nr+=n/5;
		n/=5;
	}
	return nr;
}
int caut(int x)
{
	int pas, i;
	pas = 1<<30;
	for(i=0; pas; pas>>=1)
		if(zero(i+pas)<=x)
			i=i+pas;
	if (zero (i) != x)
		return -1;
	return i-4;
}	
	
int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	int p,n;
	scanf("%d",&p);
	if (p == 0)
		printf ("1");
	else
	{
		n=caut(p);
		printf("%d",n);
	}
	return 0;
}