import java.io.*; import java.math.*; import java.util.*; import static java.util.Arrays.*; public class Main { private static final int mod = (int)1e9+7; final Random random = new Random(0); final IOFast io = new IOFast(); /// MAIN CODE public void run() throws IOException { // int TEST_CASE = Integer.parseInt(new String(io.nextLine()).trim()); int TEST_CASE = 1; while(TEST_CASE-- != 0) { double x = io.nextDouble(); double ans = Math.PI * Math.PI / 6; for (long i = (int)1e8; i > 0; i--) { ans -= 1.0/(i*i); ans += 1.0/((i+x)*(i+x)); } io.out.printf("%.10f\n", ans); } } /// TEMPLATE static int gcd(int n, int r) { return r == 0 ? n : gcd(r, n%r); } static long gcd(long n, long r) { return r == 0 ? n : gcd(r, n%r); } static void swap(T[] x, int i, int j) { T t = x[i]; x[i] = x[j]; x[j] = t; } static void swap(int[] x, int i, int j) { int t = x[i]; x[i] = x[j]; x[j] = t; } void printArrayLn(int[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); } void printArrayLn(long[] xs) { for(int i = 0; i < xs.length; i++) io.out.print(xs[i] + (i==xs.length-1?"\n":" ")); } static void dump(Object... o) { System.err.println(Arrays.deepToString(o)); } void main() throws IOException { // IOFast.setFileIO("rle-size.in", "rle-size.out"); try { run(); } catch (EndOfFileRuntimeException e) { } io.out.flush(); } public static void main(String[] args) throws IOException { new Main().main(); } static class EndOfFileRuntimeException extends RuntimeException { private static final long serialVersionUID = -8565341110209207657L; } static public class IOFast { private BufferedReader in = new BufferedReader(new InputStreamReader(System.in)); private PrintWriter out = new PrintWriter(System.out); void setFileIn(String ins) throws IOException { in.close(); in = new BufferedReader(new FileReader(ins)); } void setFileOut(String outs) throws IOException { out.flush(); out.close(); out = new PrintWriter(new FileWriter(outs)); } void setFileIO(String ins, String outs) throws IOException { setFileIn(ins); setFileOut(outs); } private static int pos, readLen; private static final char[] buffer = new char[1024 * 8]; private static char[] str = new char[500*8*2]; private static boolean[] isDigit = new boolean[256]; private static boolean[] isSpace = new boolean[256]; private static boolean[] isLineSep = new boolean[256]; static { for(int i = 0; i < 10; i++) { isDigit['0' + i] = true; } isDigit['-'] = true; isSpace[' '] = isSpace['\r'] = isSpace['\n'] = isSpace['\t'] = true; isLineSep['\r'] = isLineSep['\n'] = true; } public int read() throws IOException { if(pos >= readLen) { pos = 0; readLen = in.read(buffer); if(readLen <= 0) { throw new EndOfFileRuntimeException(); } } return buffer[pos++]; } public int nextInt() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; int ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; } public long nextLong() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); int i = 0; long ret = 0; if(str[0] == '-') { i = 1; } for(; i < len; i++) ret = ret * 10 + str[i] - '0'; if(str[0] == '-') { ret = -ret; } return ret; } public char nextChar() throws IOException { while(true) { final int c = read(); if(!isSpace[c]) { return (char)c; } } } int reads(int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } if(str.length == len) { char[] rep = new char[str.length * 3 / 2]; System.arraycopy(str, 0, rep, 0, str.length); str = rep; } str[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; } int reads(char[] cs, int len, boolean[] accept) throws IOException { try { while(true) { final int c = read(); if(accept[c]) { break; } cs[len++] = (char)c; } } catch(EndOfFileRuntimeException e) { ; } return len; } public char[] nextLine() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isLineSep); try { if(str[len-1] == '\r') { len--; read(); } } catch(EndOfFileRuntimeException e) { ; } return Arrays.copyOf(str, len); } public String nextString() throws IOException { return new String(next()); } public char[] next() throws IOException { int len = 0; str[len++] = nextChar(); len = reads(len, isSpace); return Arrays.copyOf(str, len); } // public int next(char[] cs) throws IOException { int len = 0; cs[len++] = nextChar(); len = reads(cs, len, isSpace); return len; } public double nextDouble() throws IOException { return Double.parseDouble(nextString()); } public long[] nextLongArray(final int n) throws IOException { final long[] res = new long[n]; for(int i = 0; i < n; i++) { res[i] = nextLong(); } return res; } public int[] nextIntArray(final int n) throws IOException { final int[] res = new int[n]; for(int i = 0; i < n; i++) { res[i] = nextInt(); } return res; } public int[][] nextIntArray2D(final int n, final int k) throws IOException { final int[][] res = new int[n][]; for(int i = 0; i < n; i++) { res[i] = nextIntArray(k); } return res; } public int[][] nextIntArray2DWithIndex(final int n, final int k) throws IOException { final int[][] res = new int[n][k+1]; for(int i = 0; i < n; i++) { for(int j = 0; j < k; j++) { res[i][j] = nextInt(); } res[i][k] = i; } return res; } public double[] nextDoubleArray(final int n) throws IOException { final double[] res = new double[n]; for(int i = 0; i < n; i++) { res[i] = nextDouble(); } return res; } } }