#include <bits/stdc++.h>
using namespace std;
//#include<atcoder/all>
//using namespace atcoder;
using ll = long long int;
using ull = unsigned long long int;
using ld = long double;
constexpr ll MAX = 2000000000000000000;
constexpr ld PI = 3.14159265358979;
constexpr ll MOD = 0;//2024948111;
ld dotorad(ld K){ return PI * K / 180.0; }
ld radtodo(ld K){ return K * 180.0 / PI; }
mt19937 mt;
void randinit(){ srand((unsigned)time(NULL));mt = mt19937(rand()); }

int main(){
    ll N;
    string S;
    cin >> N >> S;
    vector<vector<ll>> DP(4,vector<ll>(N + 1,MAX));
    DP[3][0] = 0;
    for(ll i = 0;i < N;i++){
        for(ll now = 0;now < 4;now++){
            ll nxt = (now * 2 + 0) % 4;
            if(now % 2 != 0 && now != 1){
                DP[nxt][i + 1] = min(DP[nxt][i + 1],DP[now][i] + ('0' != S[i]));
            }
            
        }
        for(ll now = 0;now < 4;now++){
            ll nxt = (now * 2 + 1) % 4;
            DP[nxt][i + 1] = min(DP[nxt][i + 1],DP[now][i] + ('1' != S[i]));
        }
    }
    ll ans = MAX;
    for(ll i = 0;i < 4;i++){
        ans = min(ans,DP[i][N]);
    }
    cout << ans << endl;
}