import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


int solve(int N, int[] P, string S) {
  if (S == 'W'.repeat(N).array) return 0;
  if (S[N - 1] == 'W') return -1;
  foreach (i; 0 .. N) if (P[i] == N - 1) {
    P = P[0 .. i] ~ P[i .. N];
    break;
  }
  for (int i = 0, j = 0; i < N; i = j) {
    for (; j < N && S[P[i]] == S[P[j]]; ++j) {}
    if (S[P[i]] == 'W') {
      int mx = -1;
      foreach (k; i .. j) chmax(mx, P[k]);
      if (P[i - 1] < mx && mx > P[j % N]) return 2;
    }
  }
  return 1;
}

void main() {
  /*
  debug {{
    foreach (N; 1 .. 6 + 1) {
      auto P = iota(N).array;
      do {
        auto can = new bool[1 << N];
        foreach (s; 0 .. N) foreach (h; 0 .. 1 << (N-1)) {
          int[] cuts;
          cuts ~= s;
          foreach (i; 1 .. N) if (h >> (i-1) & 1) cuts ~= (s + i);
          const len = cast(int)(cuts.length);
          cuts ~= (s + N);
          int q;
          foreach (j; 0 .. len) {
            int mx = -1;
            foreach (i; cuts[j] .. cuts[j + 1]) chmax(mx, P[i % N]);
            q |= 1 << mx;
          }
          can[q] = true;
        }
        auto dp = new int[1 << N];
        dp[] = -1;
        dp[0] = 0;
        foreach (p; 0 .. 1 << N) if (dp[p] >= 0) {
          foreach (q; 0 .. 1 << N) if (can[q]) {
            const pp = p | q;
            if (!~dp[pp] || dp[pp] > dp[p] + 1) dp[pp] = dp[p] + 1;
          }
        }
        writeln(P, ": ");
        foreach (q; 0 .. 1 << N) write(can[q] ? 1 : 0);
        writeln(": ", dp);
        assert(dp.maxElement <= 3);
        foreach (p; 1 << (N-1) .. 1 << N) assert(~dp[p]);
      } while (P.nextPermutation);
    }
  }}
  */
  
  try {
    for (; ; ) {
      const N = readInt;
      auto P = new int[N];
      foreach (i; 0 .. N) {
        P[i] = readInt - 1;
      }
      const S = readToken;
      
      const ans = solve(N, P, S);
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}