#include<fstream>
using namespace std;

#define oo 999999999

int zero(int n)
{
    int x=0,p=5;
    while(n/p!=0)
    {
		x+=n/p;
		p*=5;
	}
    return x;
}

int caut(int n)
{
    int min=0, max=oo,m,t;
    while(min<=max)
    {
		m=min+(max-min)/2;
		t=zero(m);
		if(t==n) 
			return m-m%5;
		if(t>n) 
			max=m-1;
		else 
			min=m+1;
    }
    return -1;
}

int main()
{
    int n,x;
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    fin>>n;
    if(n==0) 
		fout<<1;
    else
		fout<<caut(n);
    fin.close();
	fout.close();
}