#include<fstream>
using namespace std;

int main()
{
	ifstream fin("fact.in");
	ofstream fout("fact.out");
	
	unsigned long long p;
	
	fin >> p;
	
	if(p == 0)
	{
		fout << 1;
		return 0;
	}
	
	unsigned long long i, aux, n = 0;
	for( i = 5; p != n; i = i + 5)
	{
		aux  = i;
		while( aux % 5 == 0)
		{
			n++;
			aux =  aux / 5;
		}
	}
	
	fout <<(unsigned long long)i - 5;
	fin.close();
	fout.close();
	return 0;
}