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)

/*
*  Author: windystreet
*  Date  : 2019-04-13 20:02:03
*  Motto : Think twice, code once.
*/
#include<bits/stdc++.h>

using namespace std;

#define X first
#define Y second
#define eps  1e-5
#define gcd __gcd
#define pb push_back
#define PI acos(-1.0)
#define lowbit(x) (x)&(-x)
#define bug printf("!!!!!\n");
#define mem(x,y) memset(x,y,sizeof(x))

typedef long long LL;
typedef long double LD;
typedef pair<int,int> pii;
typedef unsigned long long uLL;

const int maxn = 100+7;
const int INF  = 1<<30;
const int mod  = 1e9+7;

string s;
string a;
void solve(){
	int n;
	while(cin>>s){
		//cin>>s;
		a = s;
		n = s.length();
		int cnt = 0;
		int ans = mod;
		for(int i=1;i<n;i++){
			if(s[i] == s[i-1]){
				if(s[i-1] == '0') s[i] = '1';
				else s[i] = '0';
				++cnt;
			}
		}
		ans = min(ans,cnt);
		cnt = 0;
		s = a;
		for(int i=n-2;i>=0;i--){
			if(s[i] == s[i+1]){
				if(s[i+1] == '0') s[i] = '1';
				else s[i] = '0';
				++cnt;
			}
		}
		ans = min(ans,cnt);
		printf("%d\n",ans );
	}


    return;
}

int main()
{
#ifndef ONLINE_JUDGE
   // freopen("F:/in.txt","r",stdin);
#endif
//    freopen("out.txt","w",stdout);
//    ios::sync_with_stdio(false);
    int t = 1;
    //scanf("%d",&t);
    while(t--){
    //    printf("Case %d: ",cas++);
        solve();
    }
    return 0;
}