#include<fstream>
using namespace std;
ifstream f("fact.in");  
ofstream g("fact.out");
long long x,m;
int verif(long long k)
{   
    int nr=0;      
    while(k)
	{         
		nr=nr+k/5;
		k=k/5;
	}
	return nr;
}
void cautbin(long long st,long long dr,long long x)
{
    long ok=0;
    while(st<=dr&&!ok)
	{
		m=(st+dr)/2;
        if(verif(m)==x)
			ok=1;            
		else
			if(x>verif(m))       
				st=m+1;
			else
				dr=m-1;
    }
	if(ok==0)
		m=-1;  
}
   int main()
{
    f>>x;
    cautbin(1,10000000,x);
	if(m!=-1)
    {
        while(m)
		{
            if(verif(m)==x)
				m--;
			else
				break;
        }
        g<<m+1;
   }
	else
		g<<m;
	return 0;
}