Problem:
Score : 100 points

Problem Statement

Takahashi wants to print a document with N pages double-sided, where two pages of data can be printed on one sheet of paper.

At least how many sheets of paper does he need?

Constraints

N is an integer.

1 \leq N \leq 100

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

5

Sample Output 1

3

By printing the 1-st, 2-nd pages on the 1-st sheet, 3-rd and 4-th pages on the 2-nd sheet, and 5-th page on the 3-rd sheet, we can print all the data on 3 sheets of paper.

Sample Input 2

2

Sample Output 2

1

Sample Input 3

100

Sample Output 3

50

Solution in Java7 (OpenJDK 1.7.0) (judge verdict: Runtime Error)

import java.util.Scanner;


public class Main {


	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ

		Scanner sc = new Scanner(System.in);
		int N = sc.nextInt();
		int M = sc.nextInt();

		boolean[] flgM = new boolean[M];
		int[] intN = new int[N];
		boolean NG = false;
		for(int i = 0; i < M; i++) {
			int s = sc.nextInt();
			int c = sc.nextInt();

			if(flgM[s-1] == false || intN[s-1] == c) {
				intN[s-1] = c;
				flgM[s-1] = true;
			} else {
				NG = true;
			}
		}
		if(NG) {
			System.out.println(-1);
		} else {
			int result = 0;
			int kakeru = 1;
			for(int i = N-1; i >= 0; i--) {
				result = result + intN[i] * kakeru;
				kakeru = kakeru * 10;
			}
			if(String.valueOf(result).length() != N) {
				result = -1;
			}
			System.out.println(result);
		}
	}

}