#include<iostream>
#include<fstream>
using namespace std;
int main()
{
	int n,p,i,nr,f;
	ifstream in("fact.in");
	ofstream out("fact.out");
	in>>p;
	for(n=1;n<=100;n++)
	{
		f=1;
		for(i=1;i<=n;i++)
			f=f*i;
		nr=0;
		while(f%10==0)
		{
			nr++;
			f=f/10;
		}
		if(nr==p)
		{
			out<<n;
			break;
		}
	}
	
	in.close();
	out.close();
	return 0;
}