#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001LL

int main(){
	
	int n;
	cin>>n;
	
	string s;
	cin>>s;
	if(n==1){
		cout<<0<<endl;
		return 0;
	}
	if(n==2){
		if(s==string(2,'0'))cout<<1<<endl;
		else cout<<0<<endl;
		return 0;
	}
	
	vector<int> dp(1<<2,Inf32);
	rep(i,1<<2){
		if(i==0)continue;
		dp[i] = 0;
		if(((i>>1)&1)!=s[0]-'0')dp[i]++;
		if(((i>>0)&1)!=s[1]-'0')dp[i]++;
	}
	for(int i=2;i<n;i++){
		vector<int> dp2(1<<2,Inf32);
		rep(j,4){
			if(dp[j]==Inf32)continue;
			rep(k,2){
				if(((j>>1)&1)==0 && k==0)continue;
				int nj = (j<<1) + k;
				nj &= 3;
				if(nj==0)continue;
				int v = dp[j];
				if(k!=s[i]-'0')v++;
				dp2[nj] = min(dp2[nj],v);
			}
		}
		swap(dp,dp2);
	}
	int ans = Inf32;
	rep(i,4)ans = min(ans,dp[i]);
	cout<<ans<<endl;
	return 0;
}