import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStream; import java.util.BitSet; import java.util.NoSuchElementException; public class Main { public static void main(String[] args) { new Main(); } public Main() { InputChecker ic = new InputChecker(System.in); java.io.PrintWriter out = new java.io.PrintWriter(System.out); solve(ic, out); out.flush(); } public void solve(InputChecker ic, java.io.PrintWriter out) { int N = ic.nextInt(1, exponent10(1, 8)); ic.nextChar(' '); int M = ic.nextInt(1, exponent10(1, 8)); ic.readNewLine(); ic.checkEOF(); if (N % 2 == 0) { if (M % 2 == 0) { out.println(0); } else { out.println(N / 4); } } else { if (M % 2 == 0) { out.println(M / 4); } else { int ans = N / 4 + M / 4; if (N % 4 == 3 && M % 4 == 3 && N >= 7 && M >= 7) ans += 2; out.println(ans); } } } public static int exponent10(int n, int e) { return n * pow(10, e); } public static long exponent10L(int n, int e) { return n * pow(10L, e); } public static int pow(int a, int b) { int ans = 1; for (int mul = a;b > 0;b >>= 1, mul *= mul) if ((b & 1) != 0) ans *= mul; return ans; } public static long pow(long a, long b) { long ans = 1; for (long mul = a;b > 0;b >>= 1, mul *= mul) if ((b & 1) != 0) ans *= mul; return ans; } public static class CharSet { private final BitSet set = new BitSet(256); public void add(char... c) { for (char i : c) set.set(i); } public void add(CharSet... s) { for (CharSet i : s) set.or(i.set); } public boolean contains(char... c) { for (char i : c) if (!set.get(i)) return false; return true; } public boolean contains(String s) { return contains(s.toCharArray()); } private static final class Chars extends CharSet { public Chars(char... c) { super.add(c); } public Chars(CharSet... s) { super.add(s); } @Override public void add(char... c) { throw new UnsupportedOperationException(); } @Override public void add(CharSet... s) { throw new UnsupportedOperationException(); } } public static final CharSet NUMBER = new Chars('0','1','2','3','4','5','6','7','8','9'); public static final CharSet LOWER = new Chars('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'); public static final CharSet UPPER = new Chars('A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'); public static final CharSet ALPHABET = new Chars(LOWER, UPPER); } public static class InputChecker { private InputStream in; private final byte[] buffer = new byte[1024]; private final byte[] undo = new byte[1024]; private int undoSize = 0; private int read = 0; private int length = 0; public InputChecker(InputStream in) { this.in = in; } public final void setInputStream(InputStream in) { this.in = in; } public final void setInputStream(File in) { try { this.in = new FileInputStream(in); } catch (FileNotFoundException e) { e.printStackTrace(); } } private boolean hasNextByte() { if (undoSize > 0) return true; if (read < length) return true; read = 0; try { length = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } return length > 0; } private byte readByte() { if (hasNextByte()) return undoSize > 0 ? undo[--undoSize] : buffer[read++]; throw new NoSuchElementException(); } private void undo(byte b) { undo[undoSize ++] = b; } private void undo(char c) { if ((c & 0xFF80) == 0) { undo((byte)c); return; } undo((byte)(c & 0x3F | 0x80)); if ((c & 0xF800) == 0) { undo((byte)(c >> 6 & 0x1F | 0xC0)); } else { undo((byte)(c >> 6 & 0x3F | 0x80)); undo((byte)(c >> 12 | 0xE0)); } } public final boolean hasNext() { return hasNextByte(); } public final char nextChar() { byte b = readByte(); if ((b & 0x80) == 0) return (char)b; if ((b & 0x20) == 0) return (char)((b & 0x1F) << 6 | (readByte() & 0x3F)); return (char)((b & 0xF) << 12 | (readByte() & 0x3F) << 6 | (readByte() & 0x3F)); } public final char nextChar(char estimate) { char c = nextChar(); if (estimate == c) return estimate; undo(c); throw new AssertionError(); } public final char nextChar(CharSet estimate) { char c = nextChar(); if (estimate.contains(c)) return c; undo(c); throw new AssertionError(); } public final void readNewLine() { char c = nextChar(); if (c == '\r') { c = nextChar(); if (c != '\n') undo(c); return; } else if (c == '\n') return; undo(c); throw new AssertionError(); } public final void checkEOF() { if (hasNextByte()) throw new AssertionError(); } public final String next(CharSet contains) { StringBuilder sb = new StringBuilder(); try { do { char c = nextChar(); if (!contains.contains(c)) { undo(c); return sb.toString(); } sb.append(c); } while(true); } catch (NoSuchElementException e) { if (sb.length() <= 0) throw new AssertionError(); return sb.toString(); } } public final int nextInt() { byte b = readByte(); int n = 0; if (b == '-') { if (!isNumber(b = readByte())) { undo(b); throw new NumberFormatException(); } try { if (b == '0') { if (!isNumber(b = readByte())) { undo(b); return 0; } throw new NumberFormatException(); } do n = Math.addExact(Math.multiplyExact(n, 10), '0' - b); while(isNumber(b = readByte())); undo(b); } catch (NoSuchElementException e) { } return n; } if (!isNumber(b)) { undo(b); throw new NumberFormatException(); } try { if (b == '0') { if (!isNumber(b = readByte())) { undo(b); return 0; } throw new NumberFormatException(); } do n = Math.addExact(Math.multiplyExact(n, 10), b - '0'); while(isNumber(b = readByte())); undo(b); } catch (NoSuchElementException e) { } return n; } public final int nextInt(int min, int max) { int n = nextInt(); if (min <= n && n <= max) return n; throw new NumberFormatException(); } private static boolean isNumber(byte c) { return '0' <= c && c <= '9'; } public final long nextLong() { byte b = readByte(); long n = 0; if (b == '-') { if (!isNumber(b = readByte())) { undo(b); throw new NumberFormatException(); } try { if (b == '0') { if (!isNumber(b = readByte())) { undo(b); return 0; } throw new NumberFormatException(); } do n = Math.addExact(Math.multiplyExact(n, 10), '0' - b); while(isNumber(b = readByte())); undo(b); } catch (NoSuchElementException e) { } return n; } if (!isNumber(b)) { undo(b); throw new NumberFormatException(); } try { if (b == '0') { if (!isNumber(b = readByte())) { undo(b); return 0; } throw new NumberFormatException(); } do n = Math.addExact(Math.multiplyExact(n, 10), b - '0'); while(isNumber(b = readByte())); undo(b); } catch (NoSuchElementException e) { } return n; } public final long nextLong(long min, long max) { long n = nextLong(); if (min <= n && n <= max) return n; throw new NumberFormatException(); } public final double nextDouble() { StringBuilder sb = new StringBuilder(); byte b = readByte(); if (b == '-') { sb.append(b); b = readByte(); } if (b == '0') { sb.append(b); b = readByte(); } else { while(isNumber(b)) { sb.append(b); b = readByte(); } } if (b == '.') { sb.append(b); b = readByte(); while(isNumber(b)) { sb.append(b); b = readByte(); } } if (b == 'e' || b == 'E') { sb.append(b); b = readByte(); if (b == '-' || b == '+') { sb.append(b); b = readByte(); } while(isNumber(b)) { sb.append(b); b = readByte(); } } undo(b); return Double.parseDouble(sb.toString()); } } }