# include <fstream>
  using namespace std;
	
	ifstream f ( "fact.in" );
	ofstream g ( "fact.out" );
	
	  int P, N;
		
		int NRz (int x) {
			int nr = 0;
			
			while (x) {
			  nr += x / 5;
				x /= 5;
			}
			
			return nr;
		}
		
		int main () {
			
			f >> P;
			
			int st, dr, mij;
			
			N = -1;
			st = 0;
			dr = 10000000;
			
			while (st <= dr) {
				mij = (st + dr) / 2;
				if (NRz(mij) == P) {N = mij; break;}
				  else if (NRz(mij) < P) st = mij + 1;
						else dr = mij - 1;
			}
			if (N != -1) {
				for (; NRz(N) == P; --N) ;
				++ N;
			}
			g << N << '\n';
			
			g.close ();
			return 0;
			
		}