import java.util.*;
import java.io.*;
import java.math.BigDecimal;

public class Main {	
	public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	}
	
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");

		public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
	
} import java.util.*; util.* java import java.io.*; io.* java import java.math.BigDecimal; BigDecimal java.math public class Main {	
	public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	}
	
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");

		public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
	
} Main public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	} main {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	} FastScanner fs = new FastScanner(); fs new FastScanner() int L = fs.nextInt(); L fs.nextInt() fs.nextInt fs double y = (double)L/3; y (double)L/3 (double)L 3 BigDecimal x = BigDecimal.valueOf(y); x BigDecimal.valueOf(y) BigDecimal.valueOf BigDecimal y BigDecimal ans = x.multiply(x); ans x.multiply(x) x.multiply x x ans = ans.multiply(x) ans ans.multiply(x) ans.multiply ans x System.out.printf("%.12f", ans) System.out.printf System.out System System.out "%.12f" ans String[] args args static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");

		public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	} FastScanner BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) StringTokenizer st=new StringTokenizer(""); st new StringTokenizer("") public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		} next {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		} while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				} !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				} catch (IOException e) {
					e.printStackTrace();
				} IOException e {
					e.printStackTrace();
				} e.printStackTrace() e.printStackTrace e {
					st=new StringTokenizer(br.readLine());
				} st=new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st public int nextInt() {
			return Integer.parseInt(next());
		} nextInt {
			return Integer.parseInt(next());
		} return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public long nextLong() {
			return Long.parseLong(next());
		} nextLong {
			return Long.parseLong(next());
		} return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		} readArray {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		} int[] a=new int[n]; a new int[n] n for (int i=0; i<n; i++) {
				a[i]=nextInt();
			} int i=0; int i=0; i 0 i<n i n i++ i++ i {
				a[i]=nextInt();
			} {
				a[i]=nextInt();
			} a[i]=nextInt() a[i] a i nextInt() nextInt return a; a int n n public double nextDouble() {
			return Double.parseDouble(next());
		} nextDouble {
			return Double.parseDouble(next());
		} return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public class Main {	
	public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	}
	
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");

		public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
	
} public class Main {	
	public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	}
	
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");

		public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
	
} Main
import java.util.*;
import java.io.*;
import java.math.BigDecimal;

public class Main {	
	public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int L = fs.nextInt();
		double y = (double)L/3;
		BigDecimal x = BigDecimal.valueOf(y);
		BigDecimal ans = x.multiply(x);
		 ans = ans.multiply(x);

		 System.out.printf("%.12f", ans);
 
	}
	
	static class FastScanner {
		BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st=new StringTokenizer("");

		public String next() {
			while (!st.hasMoreElements())
				try {
					st=new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			return st.nextToken();
		}

		public int nextInt() {
			return Integer.parseInt(next());
		}

		public long nextLong() {
			return Long.parseLong(next());
		}

		public int[] readArray(int n) {
			int[] a=new int[n];
			for (int i=0; i<n; i++) {
				a[i]=nextInt();
			}
			return a;
		}

		public double nextDouble() {
			return Double.parseDouble(next());
		}

	}
	
}
