#include<iostream.h>
#include<stdio.h>

long n,i,j;

int zero(int a)
{
	int i=5,s=0;
	
	while(i<=a)
	{ 
	s=s+a/i;
	i=i*5;
	}
	return s;
}	

int main()
{
	freopen("fact.in","r",stdin);

	freopen("fact.out","w",stdout);
	cin>>n;
	int r,l; 
	r=n*5;
	l=1;
	int j,p = 1;
	while(p!=0)
	{   
		j=(l+r)/2; 
		if ( zero(j) > n )   r=j;
		else if ( zero(j) < n )    l=j+1;
        if(zero(j)==n) 
		{
			p=0;
            l=j;
			
		}	
		if( p == 1 && l == r) 
			break;
	}
	if(p==1) cout<<"-1";
	else
	{
		if((l-5)%5!=0)  l=l-l%5;
		cout<<l;	
 	}	
	
}