#include <iostream>
#include <iomanip>
#include <fstream>
#include <string>
#include <array>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <stack>
#include <queue>
#include <bitset>
#include <tuple>
#include <cmath>
#include <complex>
#include <algorithm>
#include <utility>
#include <regex>
#include <cstdint>
#include <numeric>
#include <functional>
#include <cassert>

using namespace std;
using ll = int64_t;
using ull = uint64_t;

constexpr ll INF = 1e+15;


void solve(istream &cin) {
    string s;
    cin >> s;
    if(!cin) return;
    
    ll ans = min(count_if(s.begin(), s.end(), '0'), count_if(s.begin(), s.end(), '1'));
    cout << ans  << endl;

}

int main(int argc, char *argv[]) {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cout << setprecision(16) << scientific;
#ifdef DEBUG
    cerr << "DEBUG MODE" << endl;
    string test_cases = "test.txt";
    auto fs = fstream(test_cases, fstream::in);
    while(fs) {
        solve(fs);
    }
#else
    solve(cin);
#endif
    return 0;
}
