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

using ll = long long;
#define rep(i, n) for (ll i = 0; i < (n); i++)

bool solve() {
    ll N;
    cin >> N;
    if (N == 0) return false;
    string S;
    cin >> S;
    ll ans = 8;

    vector<ll> v = {};
    ll sum = 0;
    auto check = [&]() -> bool {
        ll m = v.size();
        set<ll> s;
        rep(msk, 1 << m) {
            ll add = 0;
            rep(j, m) {
                if ((msk >> j) & 1) add += v[j];
            }
            s.insert(add);
        }
        rep(i, N + 1) if (S[i] == 'o') {
            if (s.count(i) == 0) return false;
        }
        return true;
    };

    auto dfs = [&](auto&& self) {
        if (sum == N) {
            if (check()) {
                ans = min(ans, (ll)v.size());
            }
            return;
        }
        if (v.size() >= ans) return;
        ll b = (v.empty() ? 1 : v.back());
        for (ll add = b; sum + add <= N; add++) {
            v.push_back(add);
            sum += add;
            self(self);
            sum -= add;
            v.pop_back();
        }
    };

    dfs(dfs);

    cout << ans << endl;
    return true;
}

int main() {
    while (solve())
        ;
}