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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

#include<stdio.h>

int main(void){
    /*入力を文字列として確保*/
    char input[100000];
    for(int i=0;i<100000;i++){
        scanf("%c",&input[i]);
    }
    int length=0;
    /*入力の文字列長を確保*/
    while(input[length]=='0' || input[length]=='1'){
        length++;
    }
    /*同じサイズ、内容のint配列を作成*/
    char num[length+1];
    for(int k=0;k<=length;k++){
        num[k]=input[k]-'0';
    }
    /*比較対象二つを作成*/
    int compari[2][length+1];
    for(int l=0;l<2;l++){
        for(int m=0;m<=length;m++){
            if(m==0){
                compari[l][m]=l;
            }else{
                compari[l][m]=2-compari[l][m-1];
            }
        }
    }
    /*入力列と比較対象二つを比較し、何個異なるかをカウント*/
    int output[2]={0,0};
    for(int i=0;i<2;i++){
        for(int j=0;j<=length;j++){
            if(compari[i][j]!=num[j]){
                output[i]+=1;
            }
        }
    }
    /*どちらの比較対象だとより少ない回数で終わるか比較し出力*/
    if(output[0]>output[1]){
        printf("%d\n",output[1]);
    }else{
        printf("%d\n",output[0]);
    }
    return 0;
}