#include <bits/stdc++.h>
#ifdef CKISEKI
#define safe cerr<<__PRETTY_FUNCTION__<<" line "<<__LINE__<<" safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange(#a, a)
using std::cerr;
template <typename ...T>
void debug_(const char *s, T ...a) {
    cerr << "\e[1;32m(" << s << ") = (";
    int cnt = sizeof...(T);
    (..., (cerr << a << (--cnt ? ", " : ")\e[0m\n")));
}
template <typename I>
void orange_(const char *s, I L, I R) {
    cerr << "\e[1;32m[ " << s << " ] = [ ";
    for (int f = 0; L != R; ++L)
        cerr << (f++ ? ", " : "") << *L;
    cerr << " ]\e[0m\n";
}
#else
#define safe ((void)0)
#define debug(...) ((void)0)
#define orange(...) ((void)0)
#endif

#define all(v) begin(v),end(v)

using namespace std;

class Hash {
    private:
        static constexpr int P = 127, Q = 1051762951;
        vector<int> h, p;

        int mul(int64_t a, int64_t b) {
            return static_cast<int>(a * b % Q);
        }
        int add(int a, int b) {
            return a+b >= Q ? a+b - Q : a+b;
        }
        int sub(int a, int b) {
            return a-b < 0 ? a-b + Q : a - b;
        }
    public:
        void init(const string &s) {
            h.assign(s.size() + 1, 0); p.resize(s.size() + 1);
            for (size_t i = 0; i < s.size(); ++i)
                h[i + 1] = add(mul(h[i], P), s[i]);
            generate(p.begin(), p.end(), [x=1,y=1,this]()
                    mutable {y=x;x=mul(x,P); return y;});
        }
        int query(int l, int r) {
            return sub(h[r], mul(h[l], p[r - l]));
        }
};


Hash hs, revhs;

int main() {
    cin.tie(nullptr) -> sync_with_stdio(false);
    int N;
    string S;
    cin >> N >> S;

    hs.init(S);
    auto rS = S;
    reverse(rS.begin(), rS.end());
    revhs.init(rS);

    if (S != rS) {
        cout << 1 << '\n';
        return 0;
    }

    for (int i = 1; i <= N; i++) {
        bool prefix_pal = hs.query(0, i) == revhs.query(N-i, N);
        bool suffix_pal = hs.query(i, N) == revhs.query(0, N-i);

        if (!prefix_pal && !suffix_pal) {
            debug(S.substr(0, i), S.substr(i, N - i));
            cout << 2 << '\n';
            return 0;
        }
    }

    cout << -1 << '\n';

    return 0;
}