#include <iostream>
#include <cstdio>

using namespace std;

int zeroT;

int endZeros(int num)
{
	int c=0,i;
	for(i=5;i<=num;i*=5)
		c+=num/i;
	return c;
}

int binSearch(int l, int r)
{
	if(l==r)
	{
		if(endZeros(l)==zeroT)
			return l;
		else
			return -1;
	}
	else
	{
		int m=(l+r)/2;
		if(endZeros(m)<zeroT)
			return binSearch(m+1,r);
		else
			return binSearch(l,m);
	}
}

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

	cin>>zeroT;
	cout<<binSearch(1,500000000);

	return 0;
}