#line 2 "/Users/noya2/Desktop/Noya2_library/template/template.hpp"
using namespace std;

#include<bits/stdc++.h>
#line 1 "/Users/noya2/Desktop/Noya2_library/template/inout_old.hpp"
namespace noya2 {

template <typename T, typename U>
ostream &operator<<(ostream &os, const pair<T, U> &p){
    os << p.first << " " << p.second;
    return os;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p){
    is >> p.first >> p.second;
    return is;
}

template <typename T>
ostream &operator<<(ostream &os, const vector<T> &v){
    int s = (int)v.size();
    for (int i = 0; i < s; i++) os << (i ? " " : "") << v[i];
    return os;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &v){
    for (auto &x : v) is >> x;
    return is;
}

void in() {}
template <typename T, class... U>
void in(T &t, U &...u){
    cin >> t;
    in(u...);
}

void out() { cout << "\n"; }
template <typename T, class... U, char sep = ' '>
void out(const T &t, const U &...u){
    cout << t;
    if (sizeof...(u)) cout << sep;
    out(u...);
}

template<typename T>
void out(const vector<vector<T>> &vv){
    int s = (int)vv.size();
    for (int i = 0; i < s; i++) out(vv[i]);
}

struct IoSetup {
    IoSetup(){
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(15);
        cerr << fixed << setprecision(7);
    }
} iosetup_noya2;

} // namespace noya2
#line 1 "/Users/noya2/Desktop/Noya2_library/template/const.hpp"
namespace noya2{

const int iinf = 1'000'000'007;
const long long linf = 2'000'000'000'000'000'000LL;
const long long mod998 =  998244353;
const long long mod107 = 1000000007;
const long double pi = 3.14159265358979323;
const vector<int> dx = {0,1,0,-1,1,1,-1,-1};
const vector<int> dy = {1,0,-1,0,1,-1,-1,1};
const string ALP = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
const string alp = "abcdefghijklmnopqrstuvwxyz";
const string NUM = "0123456789";

void yes(){ cout << "Yes\n"; }
void no(){ cout << "No\n"; }
void YES(){ cout << "YES\n"; }
void NO(){ cout << "NO\n"; }
void yn(bool t){ t ? yes() : no(); }
void YN(bool t){ t ? YES() : NO(); }

} // namespace noya2
#line 2 "/Users/noya2/Desktop/Noya2_library/template/utils.hpp"

#line 6 "/Users/noya2/Desktop/Noya2_library/template/utils.hpp"

namespace noya2{

unsigned long long inner_binary_gcd(unsigned long long a, unsigned long long b){
    if (a == 0 || b == 0) return a + b;
    int n = __builtin_ctzll(a); a >>= n;
    int m = __builtin_ctzll(b); b >>= m;
    while (a != b) {
        int mm = __builtin_ctzll(a - b);
        bool f = a > b;
        unsigned long long c = f ? a : b;
        b = f ? b : a;
        a = (c - b) >> mm;
    }
    return a << std::min(n, m);
}

template<typename T> T gcd_fast(T a, T b){ return static_cast<T>(inner_binary_gcd(std::abs(a),std::abs(b))); }

long long sqrt_fast(long long n) {
    if (n <= 0) return 0;
    long long x = sqrt(n);
    while ((x + 1) * (x + 1) <= n) x++;
    while (x * x > n) x--;
    return x;
}

template<typename T> T floor_div(const T n, const T d) {
    assert(d != 0);
    return n / d - static_cast<T>((n ^ d) < 0 && n % d != 0);
}

template<typename T> T ceil_div(const T n, const T d) {
    assert(d != 0);
    return n / d + static_cast<T>((n ^ d) >= 0 && n % d != 0);
}

template<typename T> void uniq(std::vector<T> &v){
    std::sort(v.begin(),v.end());
    v.erase(unique(v.begin(),v.end()),v.end());
}

template <typename T, typename U> inline bool chmin(T &x, U y) { return (y < x) ? (x = y, true) : false; }

template <typename T, typename U> inline bool chmax(T &x, U y) { return (x < y) ? (x = y, true) : false; }

template<typename T> inline bool range(T l, T x, T r){ return l <= x && x < r; }

} // namespace noya2
#line 8 "/Users/noya2/Desktop/Noya2_library/template/template.hpp"

#define rep(i,n) for (int i = 0; i < (int)(n); i++)
#define repp(i,m,n) for (int i = (m); i < (int)(n); i++)
#define reb(i,n) for (int i = (int)(n-1); i >= 0; i--)
#define all(v) (v).begin(),(v).end()

using ll = long long;
using ld = long double;
using uint = unsigned int;
using ull = unsigned long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using pil = pair<int,ll>;
using pli = pair<ll,int>;

namespace noya2{

/*　~ (. _________ . /)　*/

}

using namespace noya2;


#line 2 "c.cpp"

#line 2 "/Users/noya2/Desktop/Noya2_library/data_structure/segment_tree.hpp"

namespace noya2{

template <class S, S (*op)(S, S), S (*e)()> struct segtree {
  public:
    segtree() : segtree(0) {}
    segtree(int n) : segtree(std::vector<S>(n, e())) {}
    segtree(const std::vector<S>& v) : _n(int(v.size())) {
        log = 0;
        size = 1;
        while (size < _n) size <<= 1, log++;

        d = std::vector<S>(2 * size, e());
        for (int i = 0; i < _n; i++) d[size + i] = v[i];
        for (int i = size - 1; i >= 1; i--) {
            update(i);
        }
    }

    void set(int p, S x) {
        assert(0 <= p && p < _n);
        p += size;
        d[p] = x;
        for (int i = 1; i <= log; i++) update(p >> i);
    }

    S get(int p) {
        assert(0 <= p && p < _n);
        return d[p + size];
    }

    S prod(int l, int r) {
        assert(0 <= l && l <= r && r <= _n);
        S sml = e(), smr = e();
        l += size;
        r += size;

        while (l < r) {
            if (l & 1) sml = op(sml, d[l++]);
            if (r & 1) smr = op(d[--r], smr);
            l >>= 1;
            r >>= 1;
        }
        return op(sml, smr);
    }

    S all_prod() { return d[1]; }

    template <bool (*f)(S)> int max_right(int l) {
        return max_right(l, [](S x) { return f(x); });
    }
    template <class F> int max_right(int l, F f) {
        assert(0 <= l && l <= _n);
        assert(f(e()));
        if (l == _n) return _n;
        l += size;
        S sm = e();
        do {
            while (l % 2 == 0) l >>= 1;
            if (!f(op(sm, d[l]))) {
                while (l < size) {
                    l = (2 * l);
                    if (f(op(sm, d[l]))) {
                        sm = op(sm, d[l]);
                        l++;
                    }
                }
                return l - size;
            }
            sm = op(sm, d[l]);
            l++;
        } while ((l & -l) != l);
        return _n;
    }

    template <bool (*f)(S)> int min_left(int r) {
        return min_left(r, [](S x) { return f(x); });
    }
    template <class F> int min_left(int r, F f) {
        assert(0 <= r && r <= _n);
        assert(f(e()));
        if (r == 0) return 0;
        r += size;
        S sm = e();
        do {
            r--;
            while (r > 1 && (r % 2)) r >>= 1;
            if (!f(op(d[r], sm))) {
                while (r < size) {
                    r = (2 * r + 1);
                    if (f(op(d[r], sm))) {
                        sm = op(d[r], sm);
                        r--;
                    }
                }
                return r + 1 - size;
            }
            sm = op(d[r], sm);
        } while ((r & -r) != r);
        return 0;
    }

  private:
    int _n, size, log;
    std::vector<S> d;

    void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); }
};

} // namespace noya2
#line 4 "c.cpp"

int op(int a, int b){
    return max(a,b);
}
int e(){
    return 0;
}

int naive(int n, vector<int> a, string s){
    assert(ssize(a) == n+1);
    assert(a[0] == n-1 && a[n] == n-1);
    vector<int> dp(n+1,0);
    repp(i,1,n){
        if (s[a[i]] == 'W') continue;
        int wma = 0, bma = -1;
        reb(j,i){
            if (s[a[j]] == 'W'){
                chmax(wma,a[j]);
                continue;
            }
            if (max(a[j],a[i]) < wma && max(a[i],a[j]) > bma){
                chmax(dp[i],dp[j]);
            }
            chmax(bma,a[j]);
        }
        dp[i]++;
    }
    // out(dp);
    // out(ranges::max(dp)); cout << flush;
    return ranges::max(dp);
}

int calc(int n, vector<int> a, string s){
    assert(ssize(a) == n+1);
    assert(a[0] == n-1 && a[n] == n-1);
    vector<int> lsb(n+1,0), rsb(n+1,n);
    vector<int> lsw(n+1,0), rsw(n+1,n);
    {
        vector<int> stb, stw;
        vector<int> idsb, idsw;
        rep(i,n+1){
            auto &st = (s[a[i]] == 'W' ? stw : stb);
            auto &ids = (s[a[i]] == 'W' ? idsw : idsb);
            while (!st.empty() && st.back() >= -a[i]){
                st.pop_back();
                ids.pop_back();
            }
            st.push_back(-a[i]);
            ids.push_back(i);
            if (s[a[i]] == 'B'){
                int posw = lower_bound(all(stw), -a[i]) - stw.begin();
                if (posw > 0){
                    lsw[i] = idsw[posw-1];
                }
                int posb = lower_bound(all(stb), -a[i]) - stb.begin();
                if (posb > 0){
                    lsb[i] = idsb[posb-1];
                }
            }
        }
    }
    {
        vector<int> stb, stw;
        vector<int> idsb, idsw;
        reb(i,n+1){
            auto &st = (s[a[i]] == 'W' ? stw : stb);
            auto &ids = (s[a[i]] == 'W' ? idsw : idsb);
            while (!st.empty() && st.back() >= -a[i]){
                st.pop_back();
                ids.pop_back();
            }
            st.push_back(-a[i]);
            ids.push_back(i);
            if (s[a[i]] == 'B'){
                int posw = lower_bound(all(stw), -a[i]) - stw.begin();
                if (posw > 0){
                    rsw[i] = idsw[posw-1];
                }
                int posb = lower_bound(all(stb), -a[i]) - stb.begin();
                if (posb > 0){
                    rsb[i] = idsb[posb-1];
                }
            }
        }
    }
    segtree<int,op,e> segand(n+1), segor(n+1);
    vector<int> dp(n+1,0);
    vector<vector<int>> updand(n+2), updor(n+2);
    repp(i,1,n+1){
        for (int j : updand[i]){
            if (j >= 0){
                segand.set(j,dp[j]);
            }
            else {
                segand.set(~j,e());
            }
        }
        for (int j : updor[i]){
            assert(j >= 0);
            segor.set(j,dp[j]);
        }
        if (s[a[i]] == 'B'){
            if (lsb[i] < lsw[i]){
                chmax(dp[i],segor.prod(lsb[i],lsw[i]));
            }
            chmax(dp[i],segand.prod(0,lsw[i]));
            dp[i]++;
            updor[rsw[i]+1].emplace_back(i);
            if (rsw[i]+1 < rsb[i]+1){
                updand[rsw[i]+1].emplace_back(i);
                updand[rsb[i]+1].emplace_back(~i);
            }
        }
    }
    // out(lsw); out(lsb);
    // out(rsw); out(rsb);
    // out(dp); cout << flush;
    return ranges::max(dp);
}


void solve(){
    int n; in(n);
    vector<int> p(n); in(p);
    rep(i,n) --p[i];
    string s; in(s);
    if (s == string(n,'W')){
        out(0);
        return ;
    }
    if (s[n-1] == 'W'){
        out(-1);
        return ;
    }
    int mapos = [&]{
        rep(i,n){
            if (p[i] == n-1){
                return i;
            }
        }
        abort();
    }();
    vector<int> a; a.reserve(n+1);
    rep(i,n+1){
        a.emplace_back(p[(mapos+i)%n]);
    }
    int ans = calc(n,a,s);
    // assert(naive(n,a,s) == ans);
    out(ans);
}

int main(){
    int t = 1; //in(t);
    while (t--) { solve(); }
}