// c++ test.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include <iostream>
#include <fstream>

using namespace std;
long long GetNumOfZeros(long long x);
long long BinarySearch(long long p);
long long CorrectAnswer(long long x);

int main()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");
	//cout << "Hello World!\n";
	long long p;
	fin >> p;
	if (p != 0)
		fout << BinarySearch(p);
	else
		fout << 1;
}


long long GetNumOfZeros(long long x)
{
	long long div = 5, sum = 0;
	while (x != 0)
	{
		x = x / div;
		sum += x;
	}
	return sum;
}

long long CorrectAnswer(long long x)
{
	long long val = GetNumOfZeros(x);
	while (GetNumOfZeros(x - 1) == val && x > 0)
		x--;
	return x;
}


long long BinarySearch(long long p)
{
	long long left = 0, right = 10000000000, mid;
	while (left < right)
	{
		mid = (left + right) / 2;
		long long num = GetNumOfZeros(mid);
		if (num >= p)
			right = mid;
		else if (num < p)
			left = mid + 1;
	}
	if (GetNumOfZeros(left) == p)
		return left;
	return -1;
}

// Run program: Ctrl + F5 or Debug > Start Without Debugging menu
// Debug program: F5 or Debug > Start Debugging menu

// Tips for Getting Started: 
//   1. Use the Solution Explorer window to add/manage files
//   2. Use the Team Explorer window to connect to source control
//   3. Use the Output window to see build output and other messages
//   4. Use the Error List window to view errors
//   5. Go to Project > Add New Item to create new code files, or Project > Add Existing Item to add existing code files to the project
//   6. In the future, to open this project again, go to File > Open > Project and select the .sln file