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 endl '\n'
#define PB push_back
#define MP make_pair
#define LL long long
#define FOR(i,a,b) for(int i = (a); i <= (b); i++)
#define RE(i,n) FOR(i,1,n)
#define REP(i,n) FOR(i,0,(int)(n)-1)
#define R(i,n) REP(i,n)
#define VI vector<int>
#define PII pair<int,int>
#define LD long double
#define FI first
#define SE second
#define st FI
#define nd SE
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())

typedef long long ll;

bool file=0,rt=1;
clock_t tStart ;
void FAST_IO();
////////////////////////

int main() {

    //FAST_IO();
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    cout << setprecision(5);
    cout << fixed;

    string s;
    cin >> s;
    int ans1 = 0;
    int ans2 = 0;
    char ch;

    int n = s.size();

    if(n < 2) {

        cout << 0 << endl;
        return 0;
    }

    ch = s[0];


    for(int i = 0; i < n; i++) {

        if(i % 2 == 0) {

            if(s[i] != ch) ans1++;
        }
        else {

            if(s[i] == ch) ans1++;
        }
    }

    if(s[0] == '1') ch = '0';
    else ch = '1';



    for(int i = 0; i < n; i++) {

        if(i % 2 == 0) {

            if(s[i] != ch) ans2++;
        }
        else {

            if(s[i] == ch) ans2++;
        }
    }

    cout << min(ans1, ans2) << endl;






    return 0;
}

void FAST_IO()
{
    ios_base::sync_with_stdio(0);
    cin.tie(NULL);
    //cout.tie(NULL);
    //cout.setf(ios::fixed);
    //cout.precision(2);
    if(rt && file){ tStart = clock(); }
    if(file){
    #ifndef _offline
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
    #endif
    }
}