#include <bits/stdc++.h>
using namespace std;

int minimumBeating(int N, string S){

    vector<int> pref1(N);
    vector<int> pref0(N);
    int sum0 =0;
    int sum1 =0;

    for(int i=0;i<N;i++){
        if(S[i]=='1'){
            sum1++;
        }
        else{
            sum0++;
        }
        pref1[i] = sum1;
        pref0[i] = sum0;
    }

    int ans = min(pref0[N-1],pref1[N-1]);

    for(int i=N;i>=1;i--){

        int start =0;
        int end = i-2;
        int rem = pref0[i-1];
        int sides = pref1[N-1]-pref1[i-1];

        ans = min(ans,max(rem,sides));

        while(start<end){
            int mid = (start+end)/2;
            int temprem = pref0[i-1]-pref0[mid+1]+(S[mid+1]=='0');
            int tempsides = pref1[N-1] - (pref1[i-1]-pref1[mid+1]+(S[mid+1]=='1'));

            if(temprem>tempsides){
                start =mid+1;
            }
            else{
                end = mid;
            }
        }
        rem = pref0[i-1]-pref0[start+1]+(S[start+1]=='0');
        sides = pref1[N-1] - (pref1[i-1]-pref1[start+1]+(S[start+1]=='1'));
        ans = min(ans,max(rem,sides));
    }

    return ans;
}


signed main() {
    int N;
    cin>>N;
    string S;
    cin>>S;

    cout<<minimumBeating(N,S)<<endl;
}