#include <iostream>
using namespace std;

int main(void) {
    int N;
    int hcnt=0;
    int bcnt=0
    string S;
    cin >> N >> S;
    for(int i=0; i<=N; ++i) {
      if(S[i]=='#' && S[i+1]=='.') ++bcnt;
      if(s[i]=='.' && s[i+1]=='#') ++hcnt;
    }
    if(hcnt>=bcnt) cout << hcnt << "\n";
    else cout << bcnt << "\n";
    return 0;
}
