import java.util.*; import java.io.*; class Main { private static final void solve() { int n = ni(); float ans = 1000; for (int i = 1; i < n; i++) { int t = 1000 - ni(); ans *= t / 1000.; } ou.println(1000 - ans); } public static void main(String[] args) { solve(); ou.flush(); } private static final ContestScanner sc = new ContestScanner(); private static final ContestPrinter ou = new ContestPrinter(); private static final int ni() { return sc.nextInt(); } private static final int[] ni(int n) { return sc.nextIntArray(n); } private static final long nl() { return sc.nextLong(); } private static final long[] nl(int n) { return sc.nextLongArray(n); } private static final String ns() { return sc.next(); } private static final double nd() { return sc.nextDouble(); } } class DSU { private int n; private int[] parentOrSize; public DSU(int n) { this.n = n; this.parentOrSize = new int[n]; java.util.Arrays.fill(parentOrSize, -1); } int merge(int a, int b) { if (!(0 <= a && a < n)) throw new IndexOutOfBoundsException("a=" + a); if (!(0 <= b && b < n)) throw new IndexOutOfBoundsException("b=" + b); int x = leader(a); int y = leader(b); if (x == y) return x; if (-parentOrSize[x] < -parentOrSize[y]) { int tmp = x; x = y; y = tmp; } parentOrSize[x] += parentOrSize[y]; parentOrSize[y] = x; return x; } boolean same(int a, int b) { if (!(0 <= a && a < n)) throw new IndexOutOfBoundsException("a=" + a); if (!(0 <= b && b < n)) throw new IndexOutOfBoundsException("b=" + b); return leader(a) == leader(b); } int leader(int a) { if (parentOrSize[a] < 0) { return a; } else { parentOrSize[a] = leader(parentOrSize[a]); return parentOrSize[a]; } } int size(int a) { if (!(0 <= a && a < n)) throw new IndexOutOfBoundsException("" + a); return -parentOrSize[leader(a)]; } ArrayList> groups() { int[] leaderBuf = new int[n]; int[] groupSize = new int[n]; for (int i = 0; i < n; i++) { leaderBuf[i] = leader(i); groupSize[leaderBuf[i]]++; } ArrayList> result = new ArrayList<>(n); for (int i = 0; i < n; i++) result.add(new ArrayList<>(groupSize[i])); for (int i = 0; i < n; i++) result.get(leaderBuf[i]).add(i); result.removeIf(ArrayList::isEmpty); return result; } } final class ContestScanner { private final InputStream in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; public ContestScanner(InputStream in) { this.in = in; } public ContestScanner() { this(System.in); } private boolean hasNextByte() { if (ptr < buflen) return true; ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } return buflen > 0; } private int readByte() { return hasNextByte() ? buffer[ptr++] : -1; } private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126; } public boolean hasNext() { while (hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte(); } public String next() { if (!hasNext()) throw new NoSuchElementException(); StringBuilder sb = new StringBuilder(); int b = readByte(); while (isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public void nextThrow(int n) { for (int i = 0; i < n; i++) this.next(); } public void nextThrow() { this.nextThrow(1); } public long nextLong() { if (!hasNext()) throw new NoSuchElementException(); long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) throw new NumberFormatException(); while (true) { if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; } else if (b == -1 || !isPrintableChar(b)) return minus ? -n : n; else throw new NumberFormatException(); b = readByte(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException(); return (int) nl; } public double nextDouble() { return Double.parseDouble(next()); } public boolean[] nextBoolean(char True) { String s = this.next(); int n = s.length(); boolean[] array = new boolean[n]; for (int i = 0; i < n; i++) array[i] = s.charAt(i) == True; return array; } public long[] nextLongArray(int length) { long[] array = new long[length]; for (int i = 0; i < length; i++) array[i] = this.nextLong(); return array; } public long[] nextLongArray(int length, java.util.function.LongUnaryOperator map) { long[] array = new long[length]; for (int i = 0; i < length; i++) array[i] = map.applyAsLong(this.nextLong()); return array; } public long[] nextLongArray(int length, long[] a) { long[] array = new long[length + a.length]; for (int i = 0; i < length; i++) array[i] = this.nextLong(); for (int i = length; i < array.length; i++) array[i] = a[i - length]; return array; } public int[] nextIntArray(int length) { int[] array = new int[length]; for (int i = 0; i < length; i++) array[i] = this.nextInt(); return array; } public int[] nextIntArray(int length, java.util.function.IntUnaryOperator map) { int[] array = new int[length]; for (int i = 0; i < length; i++) array[i] = map.applyAsInt(this.nextInt()); return array; } public int[] nextIntArray(int length, int[] array) { int n = length + array.length; int[] a = new int[n]; for (int i = 0; i < length; i++) a[i] = this.nextInt(); for (int i = length; i < n; i++) a[i] = array[i - length]; return a; } public Integer[] nextIntegerArray(int length, java.util.function.IntUnaryOperator map) { Integer[] array = new Integer[length]; for (int i = 0; i < length; i++) array[i] = map.applyAsInt(this.nextInt()); return array; } public Integer[] nextIntegerArray(int length) { Integer[] array = new Integer[length]; for (int i = 0; i < length; i++) array[i] = this.nextInt(); return array; } public double[] nextDoubleArray(int length) { double[] array = new double[length]; for (int i = 0; i < length; i++) array[i] = this.nextDouble(); return array; } public double[] nextDoubleArray(int length, java.util.function.DoubleUnaryOperator map) { double[] array = new double[length]; for (int i = 0; i < length; i++) array[i] = map.applyAsDouble(this.nextDouble()); return array; } public String[] nextArray(int length) { String[] array = new String[length]; for (int i = 0; i < length; i++) array[i] = this.next(); return array; } public long[][] nextLongMatrix(int height, int width) { long[][] mat = new long[height][width]; for (int h = 0; h < height; h++) for (int w = 0; w < width; w++) mat[h][w] = this.nextLong(); return mat; } public long[][] nextLongMatrix(int height, int width, java.util.function.LongUnaryOperator map) { long[][] mat = new long[height][width]; for (int h = 0; h < height; h++) for (int w = 0; w < width; w++) mat[h][w] = map.applyAsLong(this.nextLong()); return mat; } public int[][] nextIntMatrix(int height, int width) { int[][] mat = new int[height][width]; for (int h = 0; h < height; h++) for (int w = 0; w < width; w++) mat[h][w] = this.nextInt(); return mat; } public int[][] nextIntMatrix(int height, int width, java.util.function.IntUnaryOperator map) { int[][] mat = new int[height][width]; for (int h = 0; h < height; h++) for (int w = 0; w < width; w++) mat[h][w] = map.applyAsInt(this.nextInt()); return mat; } public double[][] nextDoubleMatrix(int height, int width) { double[][] mat = new double[height][width]; for (int h = 0; h < height; h++) for (int w = 0; w < width; w++) mat[h][w] = this.nextDouble(); return mat; } public boolean[][] nextBooleanMatrix(int height, int width, char True) { boolean[][] mat = new boolean[height][width]; for (int h = 0; h < height; h++) { String s = this.next(); for (int w = 0; w < width; w++) mat[h][w] = s.charAt(w) == True; } return mat; } public char[][] nextCharMatrix(int height, int width) { char[][] mat = new char[height][width]; for (int h = 0; h < height; h++) { String s = this.next(); for (int w = 0; w < width; w++) mat[h][w] = s.charAt(w); } return mat; } } final class ContestPrinter extends PrintWriter { public ContestPrinter(PrintStream stream) { super(stream); } public ContestPrinter() { super(System.out); } private static String dtos(double x, int n) { StringBuilder sb = new StringBuilder(); if (x < 0) { sb.append('-'); x = -x; } x += Math.pow(10, -n) / 2; sb.append((long) x); sb.append("."); x -= (long) x; for (int i = 0; i < n; i++) { x *= 10; sb.append((int) x); x -= (int) x; } return sb.toString(); } @Override public void print(float f) { super.print(dtos(f, 20)); } @Override public void println(float f) { super.println(dtos(f, 20)); } @Override public void print(double d) { super.print(dtos(d, 20)); } @Override public void println(double d) { super.println(dtos(d, 20)); } public void printlnArray(String[] array) { for (String i : array) super.println(i); } public void printSpace(Object... o) { int n = o.length - 1; for (int i = 0; i < n; i++) { super.print(o[i]); super.print(" "); } super.println(o[n]); } public void println(Object... o) { int n = o.length - 1; for (int i = 0; i < n; i++) super.print(o[i]); super.println(o[n]); } public void printYN(boolean o) { super.println(o ? "Yes" : "No"); } public void print(Object... o) { int n = o.length - 1; for (int i = 0; i < n; i++) super.print(o[i]); super.print(o[n]); } public void printArray(Object[] array) { int n = array.length - 1; for (int i = 0; i < n; i++) { super.print(array[i]); super.print(" "); } super.println(array[n]); } public void printlnArray(Object[] array) { for (Object i : array) super.println(i); } public void printArray(int[] array, String separator) { int n = array.length - 1; if (n == -1) return; for (int i = 0; i < n; i++) { super.print(array[i]); super.print(separator); } super.println(array[n]); } public void printArray(int[] array) { this.printArray(array, " "); } public void printArray(Integer[] array) { this.printArray(array, " "); } public void printArray(Integer[] array, String separator) { int n = array.length - 1; for (int i = 0; i < n; i++) { super.print(array[i]); super.print(separator); } super.println(array[n]); } public void printlnArray(int[] array) { for (int i : array) super.println(i); } public void printArray(int[] array, String separator, java.util.function.IntUnaryOperator map) { int n = array.length - 1; for (int i = 0; i < n; i++) { super.print(map.applyAsInt(array[i])); super.print(separator); } super.println(map.applyAsInt(array[n])); } public void printlnArray(int[] array, java.util.function.IntUnaryOperator map) { for (int i : array) super.println(map.applyAsInt(i)); } public void printlnArray(long[] array, java.util.function.LongUnaryOperator map) { for (long i : array) super.println(map.applyAsLong(i)); } public void printArray(int[] array, java.util.function.IntUnaryOperator map) { this.printArray(array, " ", map); } public void printArray(long[] array, String separator) { int n = array.length - 1; for (int i = 0; i < n; i++) { super.print(array[i]); super.print(separator); } super.println(array[n]); } public void printArray(long[] array) { this.printArray(array, " "); } public void printlnArray(long[] array) { for (long i : array) super.println(i); } public void printArray(double[] array) { printArray(array, " "); } public void printArray(double[] array, String separator) { int n = array.length - 1; for (int i = 0; i < n; i++) { super.print(array[i]); super.print(separator); } super.println(array[n]); } public void printlnArray(double[] array) { for (double i : array) super.println(i); } public void printArray(boolean[] array, String a, String b) { int n = array.length - 1; for (int i = 0; i < n; i++) super.print((array[i] ? a : b) + " "); super.println(array[n] ? a : b); } public void printArray(boolean[] array) { this.printArray(array, "Y", "N"); } public void printArray(char[] array) { for (char c : array) this.print(c); this.println(); } public void printArray(long[] array, String separator, java.util.function.LongUnaryOperator map) { int n = array.length - 1; for (int i = 0; i < n; i++) { super.print(map.applyAsLong(array[i])); super.print(separator); } super.println(map.applyAsLong(array[n])); } public void printArray(long[] array, java.util.function.LongUnaryOperator map) { this.printArray(array, " ", map); } public void printArray(ArrayList array) { this.printArray(array, " "); } public void printArray(ArrayList array, String separator) { int n = array.size() - 1; if (n == -1) return; for (int i = 0; i < n; i++) { super.print(array.get(i).toString()); super.print(separator); } super.println(array.get(n).toString()); } public void printlnArray(ArrayList array) { int n = array.size(); for (int i = 0; i < n; i++) super.println(array.get(i).toString()); } public void printlnArray(ArrayList array, java.util.function.IntUnaryOperator map) { int n = array.size(); for (int i = 0; i < n; i++) super.println(map.applyAsInt(array.get(i))); } public void printlnArray(ArrayList array, java.util.function.LongUnaryOperator map) { int n = array.size(); for (int i = 0; i < n; i++) super.println(map.applyAsLong(array.get(i))); } public void printArray(int[][] array) { for (int[] a : array) this.printArray(a); } public void printArray(int[][] array, java.util.function.IntUnaryOperator map) { for (int[] a : array) this.printArray(a, map); } public void printArray(long[][] array) { int n = array.length; if (n == 0) return; int m = array[0].length - 1; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) super.print(array[i][j] + " "); super.println(array[i][m]); } } public void printArray(long[][] array, java.util.function.LongUnaryOperator map) { int n = array.length; if (n == 0) return; int m = array[0].length - 1; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { super.print(map.applyAsLong(array[i][j])); super.print(" "); } super.println(map.applyAsLong(array[i][m])); } } public void printArray(boolean[][] array) { int n = array.length; if (n == 0) return; int m = array[0].length - 1; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) super.print(array[i][j] ? "○ " : "× "); super.println(array[i][m] ? "○" : "×"); } } public void printArray(char[][] array) { int n = array.length; if (n == 0) return; int m = array[0].length; for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) super.print(array[i][j]); super.println(); } } }