Problem:
Score : 300 points

Problem Statement

Snuke loves puzzles.

Today, he is working on a puzzle using S- and c-shaped pieces.
In this puzzle, you can combine two c-shaped pieces into one S-shaped piece, as shown in the figure below:

Snuke decided to create as many Scc groups as possible by putting together one S-shaped piece and two c-shaped pieces.

Find the maximum number of Scc groups that can be created when Snuke has N S-shaped pieces and M c-shaped pieces.

Constraints

1 ≤ N,M ≤ 10^{12}

Input

The input is given from Standard Input in the following format:

N M

Output

Print the answer.

Sample Input 1

1 6

Sample Output 1

2

Two Scc groups can be created as follows:

Combine two c-shaped pieces into one S-shaped piece

Create two Scc groups, each from one S-shaped piece and two c-shaped pieces

Sample Input 2

12345 678901

Sample Output 2

175897

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.*;
import java.util.InputMismatchException;

public class Main {

	public static void main(String[] args) {
		InputReader in = new InputReader(System.in);
		PrintWriter out = new PrintWriter(System.out);

		int n=in.nextInt();
		int m=in.nextInt();
        int ans;

        if(n*2 >= m) {
            ans = m/2;
        } else {
            ans = n;
            m -= n*2;
            ans += m/4;
        }

		out.println(ans);
		out.flush();
	}
	private static int bt(boolean[][] e, Deque<Integer> st, int pos, int cnt) {
		// System.out.println(st.toString());
		if(st.size() == e[0].length-1){
			return cnt+1;
		}
		int bef = st.peek();
		Deque<Integer> lst = new ArrayDeque<Integer>();
		for(int i=1; i<e[bef].length; i++) {
			if(e[bef][i] && !st.contains(i)) {
				lst.push(i);
				//System.out.print("i: ");
				//System.out.println(i);
			}
		}
		// for(int j=0; j<lst.size(); j++) {
		for(int j=0; j<lst.size(); ) {
			int next = lst.pop();
			st.push(next);
			cnt = bt(e, st, next, cnt);

			//System.out.print("toString");
			//System.out.println(st.toString());
			//System.out.println();
			//System.out.print("j: ");
			//System.out.print(j);
			//System.out.print(", lst.size: ");
			//System.out.println(lst.size());
			//System.out.print(", cnt: ");
			//System.out.println(cnt);
			st.pop();
		}

		return cnt;
	}

	// ----------------------

	static class InputReader {
		private InputStream stream;
		private byte[] buf = new byte[1024];
		private int curChar;
		private int numChars;

		public InputReader(InputStream stream) {
			this.stream = stream;
		}

		private int next() {
			if (numChars == -1)
				throw new InputMismatchException();
			if (curChar >= numChars) {
				curChar = 0;
				try {
					numChars = stream.read(buf);
				} catch (IOException e) {
					throw new InputMismatchException();
				}
				if (numChars <= 0)
					return -1;
			}
			return buf[curChar++];
		}

		public char nextChar() {
			int c = next();
			while (isSpaceChar(c))
				c = next();
			if (('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z')) {
				return (char) c;
			}
			throw new InputMismatchException();
		}

		public String nextToken() {
			int c = next();
			while (isSpaceChar(c))
				c = next();
			StringBuilder res = new StringBuilder();
			do {
				res.append((char) c);
				c = next();
			} while (!isSpaceChar(c));
			return res.toString();
		}

		public int nextInt() {
			int c = next();
			while (isSpaceChar(c))
				c = next();
			int sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = next();
			}
			int res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c-'0';
				c = next();
			} while (!isSpaceChar(c));
			return res*sgn;
		}

		public long nextLong() {
			int c = next();
			while (isSpaceChar(c))
				c = next();
			long sgn = 1;
			if (c == '-') {
				sgn = -1;
				c = next();
			}
			long res = 0;
			do {
				if (c < '0' || c > '9')
					throw new InputMismatchException();
				res *= 10;
				res += c-'0';
				c = next();
			} while (!isSpaceChar(c));
			return res*sgn;
		}

		public double nextDouble() {
			return Double.valueOf(nextToken());
		}

		public boolean isSpaceChar(int c) {
			return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
		}

		//public interface SpaceCharFilter {
		//	public boolean isSpaceChar(int ch);
		//}
	}
	// 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 <T> 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;  }
}