#include <fstream.h>
#include <math.h>

unsigned long p;
unsigned long log5( unsigned long k );

int main()
{
	unsigned long  i, cinci = 0;
	ifstream fin("fact.in");
	fin >> p;
	fin.close();
	for( i = 0; cinci < p - 1 ; i = i + 5 )
		cinci += log5( i );
	ofstream fout( "fact.out");
	if( p == 0 )
		fout << 1;
	else
		fout << i;
	fout.close();
	return 0;
}

unsigned long log5( unsigned long k )
{
	unsigned long rez = 0;
	while (k % 5 == 0 && k != 0 )
	{
		rez++;
		k /= 5;
	}
	return rez;
}