#include <fstream>
using namespace std;

int solve( int p ) {
	int i = 0, k = 0;

	if( p == 0 ) return 1;
	if( p == 1 ) return 5;

	while( p > 0 ) {
		i += 5;
		k++;
		if( k % 5 == 0 ) p -= k / 5;
		p--;
	}

	if( p < 0 ) return -1;

	return i;
}

int main() {
	int p;

	fstream f( "fact.in", ios::in );
	f >> p;

	fstream g( "fact.out", ios::out );
	g << solve( p );

	return 0;
}