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

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n;
    string s;
    cin >> n >> s;
    constexpr array<int,4> S = {0b011, 0b101, 0b110, 0b111};
    array<int, 8> dp{}, ndp;
    for(int i = 0; i < n; i++){
        ndp.fill(1 << 30);
        int c = s[i] - '0';
        for(auto U : S){
            int NU = U / 2 + 4 * c;
            ndp[NU] = min(ndp[NU], dp[U]);
            ndp[NU ^ 4] = min(ndp[NU ^ 4], dp[U] + 1);
        }
        dp = ndp;
    }
    int ans = 1 << 30;
    for(auto U : S) ans = min(ans, dp[U]);
    cout << ans << '\n';
}