#include <bits/stdc++.h>

using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    ifstream in("freddy.in");
    ofstream out("freddy.out");
    int n;
    string s;
    in >> n;
    in >> s;
    int cnt1 = 0, cnt0 = 0, fidx = 0, br = 1, sz = s.size();
    n = sz;
    for(int i = 1;i < n;i++){
        if(s[i] == s[i - 1]) br++;
        else{
            if(fidx == 0){
                if(s[fidx] != '0') cnt1++;
            }
            else{
                if(s[i - 1] == '0') cnt0++;
                else cnt1++;
            }
            br = 1;
            fidx = i;
        }
    }
    if(fidx == 0){
        if(s[fidx] != '0') cnt1++;
    }
    else{
        if(s[n - 1] == '0') cnt0++;
        else cnt1++;
    }
    out << min(cnt0, cnt1) << endl;
    return 0;
}