# include <fstream>
# define LL long long
  using namespace std;
	
	ifstream f ( "fact.in" );
	ofstream g ( "fact.out" );
	
	  LL P, N;
		
		int main () {
			
			f >> P;
			
			LL i, p, nr;
			
			
			for (i = 0; ; i += 5) {
				
				p = 5;
				nr = 0;
				
				while (p <= i) {
					
					nr += i / p;
					p *= 5;
					
				}
				
				if (nr == P) break;
			}
			
			g << i << '\n';
			
			g.close ();
			return 0;
			
		}