#include<stdio.h>
int factorial (int n){
	int s=0;
	while(n)
	{
		s = s+ n/5;
		n/=5;
	}
	return s;
}

int main()
{
	freopen("fact.in","r",stdin);
	freopen("fact.out","w",stdout);
	int m,d,st,k;
	printf("k=\n");
	scanf("%d",&k);
	st=1;
	d=5*100000000;
	while(st!=d)
	{
	m=(d+st)/2;
	if(factorial(m)>=k)
		d=m;
	else
		st=m+1;
	}
	if(factorial(st)==k)
		printf("%d",st);
	else
		printf("-1");
	return 0;
}