Problem: Vova and Marina love offering puzzles to each other. Today Marina offered Vova to cope with the following task.

Vova has a non-directed graph consisting of n vertices and m edges without loops and multiple edges. Let's define the operation of contraction two vertices a and b that are not connected by an edge. As a result of this operation vertices a and b are deleted and instead of them a new vertex x is added into the graph, and also edges are drawn from it to all vertices that were connected with a or with b (specifically, if the vertex was connected with both a and b, then also exactly one edge is added from x to it). Thus, as a result of contraction again a non-directed graph is formed, it contains no loops nor multiple edges, and it contains (n - 1) vertices.

Vova must perform the contraction an arbitrary number of times to transform the given graph into a chain of the maximum length. A chain of length k (k ≥ 0) is a connected graph whose vertices can be numbered with integers from 1 to k + 1 so that the edges of the graph connect all pairs of vertices (i, i + 1) (1 ≤ i ≤ k) and only them. Specifically, the graph that consists of one vertex is a chain of length 0. The vertices that are formed as a result of the contraction are allowed to be used in the following operations of contraction.

<image> The picture illustrates the contraction of two vertices marked by red.

Help Vova cope with his girlfriend's task. Find the maximum length of the chain that can be obtained from the resulting graph or else determine that it is impossible to obtain the chain.

Input

The first line contains two integers n, m (1 ≤ n ≤ 1000, 0 ≤ m ≤ 100 000) — the number of vertices and the number of edges in the original graph.

Next m lines contain the descriptions of edges in the format ai, bi (1 ≤ ai, bi ≤ n, ai ≠ bi), which means that there is an edge between vertices ai and bi. It is guaranteed that there is at most one edge between each pair of vertexes.

Output

If it is impossible to obtain a chain from the given graph, print  - 1. Otherwise, print the maximum possible number of edges in the resulting chain.

Examples

Input

5 4
1 2
2 3
3 4
3 5


Output

3


Input

4 6
1 2
2 3
1 3
3 4
2 4
1 4


Output

-1


Input

4 2
1 3
2 4


Output

2

Note

In the first sample test you can contract vertices 4 and 5 and obtain a chain of length 3.

In the second sample test it is initially impossible to contract any pair of vertexes, so it is impossible to achieve the desired result.

In the third sample test you can contract vertices 1 and 2 and obtain a chain of length 2.

Solution (in JAVA):

Solution:
import java.io.BufferedWriter;
import java.util.InputMismatchException;
import java.util.NoSuchElementException;
import java.math.BigInteger;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.io.Writer;
import java.io.IOException;
import java.util.Arrays;
import java.io.InputStream;
import java.io.OutputStreamWriter;
import java.util.Comparator;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 * @author Egor Kulikov (egor@egork.net)
 */
public class Main {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		OutputWriter out = new OutputWriter(outputStream);
		TaskE solver = new TaskE();
		solver.solve(1, in, out);
		out.close();
	}
}

class TaskE {
    public void solve(int testNumber, InputReader in, OutputWriter out) {
int count = in.readInt();
        int edgeCount = in.readInt();
        int[][] distance = new int[count][count];
        ArrayUtils.fill(distance, Integer.MAX_VALUE / 2);
        for (int i = 0; i < count; i++) {
            distance[i][i] = 0;
        }
for (int i = 0; i < edgeCount; i++) {
int from = in.readInt() - 1;
            int to = in.readInt() - 1;
            distance[from][to] = distance[to][from] = 1;
        }
        for (int i = 0; i < count; i++) {
            for (int j = 0; j < i; j++) {
                for (int k = j + 1; k < i; k++) {
                    distance[j][k] = Math.min(distance[j][k], distance[j][i] + distance[k][i]);
                }
            }
            for (int j = i + 1; j < count; j++) {
                for (int k = j + 1; k < count; k++) {
                    distance[j][k] = Math.min(distance[j][k], distance[i][j] + distance[i][k]);
                }
            }
            for (int j = 0; j < i; j++) {
                for (int k = i + 1; k < count; k++) {
                    distance[j][k] = Math.min(distance[j][k], distance[j][i] + distance[i][k]);
                }
            }
}
        for (int i = 0; i < count; i++) {
            for (int j = 0; j < i; j++) {
                distance[i][j] = distance[j][i];
            }
        }
        int answer = 0;
        boolean[] processed = new boolean[count];
        for (int i = 0; i < count; i++) {
            if (processed[i]) {
                continue;
            }
            IntList curList = new IntArrayList();
            for (int j = 0; j < count; j++) {
                if (distance[i][j] != Integer.MAX_VALUE / 2) {
                    curList.add(j);
                    processed[j] = true;
                }
            }
            int[] current = curList.toArray();
            int max = 0;
            for (int j : current) {
                for (int k : current) {
                    if ((distance[i][j] + distance[i][k] + distance[j][k]) % 2 == 1) {
                        out.printLine(-1);
                        return;
                    }
                    max = Math.max(max, distance[j][k]);
                }
            }
            answer += max;
        }
        out.printLine(answer);
    }
}

class InputReader {

	private InputStream stream;
	private byte[] buf = new byte[1024];
	private int curChar;
	private int numChars;
	private SpaceCharFilter filter;

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

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

	public boolean isSpaceChar(int c) {
		if (filter != null)
			return filter.isSpaceChar(c);
		return isWhitespace(c);
	}

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

	public interface SpaceCharFilter {
		public boolean isSpaceChar(int ch);
	}
}

class OutputWriter {
	private final PrintWriter writer;

	public OutputWriter(OutputStream outputStream) {
		writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
	}

	public void close() {
		writer.close();
	}

	public void printLine(int i) {
		writer.println(i);
	}
}

class ArrayUtils {

	public static void fill(int[][] array, int value) {
		for (int[] row : array)
			Arrays.fill(row, value);
	}

}

abstract class IntList extends IntCollection implements Comparable<IntList> {

	public abstract int get(int index);

	public IntIterator iterator() {
		return new IntIterator() {
			private int size = size();
			private int index = 0;

			public int value() throws NoSuchElementException {
				if (!isValid())
					throw new NoSuchElementException();
				return get(index);
			}

			public void advance() throws NoSuchElementException {
				if (!isValid())
					throw new NoSuchElementException();
				index++;
			}

			public boolean isValid() {
				return index < size;
			}
		};
	}

	public int hashCode() {
		int hashCode = 1;
		for (IntIterator i = iterator(); i.isValid(); i.advance())
			hashCode = 31 * hashCode + i.value();
		return hashCode;
	}

	public boolean equals(Object obj) {
		if (!(obj instanceof IntList))
			return false;
		IntList list = (IntList)obj;
		if (list.size() != size())
			return false;
		IntIterator i = iterator();
		IntIterator j = list.iterator();
		while (i.isValid()) {
			if (i.value() != j.value())
				return false;
			i.advance();
			j.advance();
		}
		return true;
	}

	public int compareTo(IntList o) {
		IntIterator i = iterator();
		IntIterator j = o.iterator();
		while (true) {
			if (i.isValid()) {
				if (j.isValid()) {
					if (i.value() != j.value()) {
						if (i.value() < j.value())
							return -1;
						else
							return 1;
					}
				} else
					return 1;
			} else {
				if (j.isValid())
					return -1;
				else
					return 0;
			}
			i.advance();
			j.advance();
		}
	}

}

class IntArrayList extends IntList {
	private int[] array;
	private int size;

	public IntArrayList() {
		this(10);
	}

	public IntArrayList(int capacity) {
		array = new int[capacity];
	}

	public int get(int index) {
		if (index >= size)
			throw new IndexOutOfBoundsException();
		return array[index];
	}

	public int size() {
		return size;
	}

	public void add(int value) {
		ensureCapacity(size + 1);
		array[size++] = value;
	}

	public void ensureCapacity(int newCapacity) {
		if (newCapacity > array.length) {
			int[] newArray = new int[Math.max(newCapacity, array.length << 1)];
			System.arraycopy(array, 0, newArray, 0, size);
			array = newArray;
		}
	}

	public int[] toArray() {
		int[] array = new int[size];
		System.arraycopy(this.array, 0, array, 0, size);
		return array;
	}

}

abstract class IntCollection {
	public abstract IntIterator iterator();
	public abstract int size();
	public abstract void add(int value);

	public int[] toArray() {
		int size = size();
		int[] array = new int[size];
		int i = 0;
		for (IntIterator iterator = iterator(); iterator.isValid(); iterator.advance())
			array[i++] = iterator.value();
		return array;
	}

}

interface IntIterator {
	public int value() throws NoSuchElementException;
	public void advance() throws NoSuchElementException;
	public boolean isValid();
}