Problem:
Score : 300 points

Problem Statement

N tiles are arranged in a row from left to right. The initial color of each tile is represented by a string S of length N.

The i-th tile from the left is painted black if the i-th character of S is 0, and painted white if that character is 1.

You want to repaint some of the tiles black or white, so that any two adjacent tiles have different colors.

At least how many tiles need to be repainted to satisfy the condition?

Constraints

1 \leq |S| \leq 10^5

S_i is 0 or 1.

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of tiles that need to be repainted to satisfy the condition.

Sample Input 1

000

Sample Output 1

1

The condition can be satisfied by repainting the middle tile white.

Sample Input 2

10010010

Sample Output 2

3

Sample Input 3

0

Sample Output 3

0

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;
import java.lang.*;

public class Main {
	
	public static void main(String[] args) {
		FastScanner sc = new FastScanner();
		out = new PrintWriter(new BufferedOutputStream(System.out));
		String s=sc.next();
		int n=s.length();
		
		int x=0;
		int y=0;
		for (int i = 0; i < n; i++) {
			if(i%2==0&&s.charAt(i)=='1') {
				x++;
			}
			if(i%2==1&&s.charAt(i)=='0') {
				x++;
			}
			
		}
		for (int i = 0; i < n; i++) {
			if(i%2==1&&s.charAt(i)=='1') {
				y++;
			}
			if(i%2==0&&s.charAt(i)=='0') {
				y++;
			}
		}
		
		out.println(Math.min(x,y));
		out.close();
	}
	static int gcd(int a,int b) {
		if(a==0) {
			return b;
		}
		return gcd(b%a,a);
	
	}

	
	
	
	
//----------------------------------------------------------
	static int l_min(int[] a) {
		Arrays.sort(a);
		return a[0];
	}
	static int l_max(int[] a) {
		int l=a.length;
		Arrays.sort(a);
		return a[l-1];
	}
	public static PrintWriter out;

	public static class MyScanner {
		BufferedReader br;
		StringTokenizer st;

		public MyScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (IOException e) {
					e.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());
		}

		long nextLong() {
			return Long.parseLong(next());
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			return str;
		}

	}
	
}


class UnionFind{
	int parent[];
	int rank[];
	int size[];
	UnionFind(int n) {
		parent=new int[n];
		rank=new int[n];
		size=new int[n];
		for(int i=0;i<n;i++) {
			parent[i]=i;
			rank[i]=0;
			size[i]=1;
		}
	}
	
	void union(int x,int y) {
		int xRoot=find(x);
		int yRoot=find(y);


		if(xRoot!=yRoot) {
			
			if(rank[xRoot]>rank[yRoot]) {
				parent[yRoot]=xRoot;
				size[xRoot]+=size[yRoot];
				
			}else if(rank[xRoot]<rank[yRoot]){
				parent[xRoot]=yRoot;
				size[yRoot]+=size[xRoot];
				
			}else {
				parent[yRoot]=xRoot;
				rank[xRoot]++;
				size[xRoot]+=size[yRoot];
			}
		}
		
	}
	
	int find(int x) {
		if(parent[x]==x) {
			return x;
		}else {
			return find(parent[x]);
		}
		
	}
	
	boolean same(int x,int y) {
		return find(x)==find(y);
	}
	
	
	
}





class FastScanner {
    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;
    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }
    private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -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 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());}
}