#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using ll   = long long;
#define rep(i, n) for (ll i = 0; i < (n); i++)
#define reps(i, a, b) for (ll i = (a); i < (b); i++)
bool chmin(auto &a, auto b) { return a > b ? a = b, 1 : 0; }
bool chmax(auto &a, auto b) { return a < b ? a = b, 1 : 0; }
vector<ll> sin45 = {0, 1, 1, 1, 0, -1, -1, -1}, cos45 = {1, 1, 0, -1, -1, -1, 0, 1};
vector<ll> dx = {0, 1, 0, -1};
vector<ll> dy = {1, 0, -1, 0};
#define ft first
#define sd second
#define all(x) std::begin(x), std::end(x)
#define mp(a, b) make_pair(a, b)
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pb(x) push_back(x)
#define so(z) sort(z.begin(), z.end())
#define sor(z) sort(z.rbegin(), z.rend())
#define vec vector<ll>
#define vecc vector<vector<ll>>

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);

    ll n;
    string s;
    cin >> n >> s;

    // 多分2個前までしか影響しない?

    vec dp(n + 5, 0);

    ll cnt = 0;

    rep(i, n) {
        if (s[i] == '1') {
            dp[i + 3] = dp[i + 2];
        } else {
            cnt ++;
            dp[i + 3] = max(dp[i] + 1, dp[i + 1]);// 0をそのままにできる、残せるなら+1、1に変えるならそのまま
        }
    }

    cout << cnt - dp[n + 2] << endl;
}