#include<fstream>
#include<iostream>
using namespace std;

ifstream in("fact.in");
ofstream out("fact.out");


int inline sum(int n)
{
	return (n-1)/4;
}

int fact(int p)
{
	if(p==0)
		return 1;
	else if(p==1)
		return 5;
	else if(p==2)
		return 10;
	else
	{
		int n=11;
		int x=5;
		int c=0;
		double v;
		do
		{
			c=0;
			for(;n/x!=0;x=x*5)
				c=c + n/x;
			++n;
			x=5;
		}while(c<p);

		if(c==p)
			return n-1;
		return -1;
	}
}
int main()
{
	int p;
	in>>p;
	out<<fact(p);
	return 0;
}