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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
#define int           long long
#define pb            push_back
#define mp            make_pair
#define PI            3.14159265
#define M             1000000007
#define MM            998244353
#define fr            first
#define sc            second
#define all(v)        (v).begin(),(v).end()
#define rall(v)       (v).rbegin(),v.rend()
#define vc            vector
#define vi            vector<int>
#define pii           pair<int,int>
#define psi           pair<string,int>
#define pis           pair<int,string>
#define mii           map<int,int>
#define msi           map<string,int>

int ans1,ans2;
int solve(){
    string str; cin>>str;
    for (int i = 0; i < str.length(); ++i)
    {
        if(i%2){
            if(str[i]=='0') ans1++;
            else ans2++;
        }
        else{
            if(str[i]=='0') ans2++;
            else ans1++;
        }
    }
    cout<<min(ans1,ans2);
    return 0;
}

signed main() {
    ios::sync_with_stdio(false);
    //freopen("input.txt", "r", stdin);
    //freopen("output.txt", "w", stdout);
    int t=1;
    //cin>>t;
    while(t--) solve();
    return 0;
}