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)); }


// root: max (tie-break: left)
class MaxCartesianTree {
  int n, rt;
  int[] par, lef, rig;
  void build(T)(T as) {
    n = cast(int)(as.length);
    assert(n >= 1);
    rt = 0;
    par = new int[n]; par[] = -1;
    lef = new int[n]; lef[] = -1;
    rig = new int[n]; rig[] = -1;
    int top = 0;
    auto stack = new int[n];
    foreach (u; 1 .. n) {
      if (as[stack[top]] < as[u]) {  // <
        for (; top >= 1 && as[stack[top - 1]] < as[u]; --top) {}  // <
        if (top == 0) {
          rt = par[lef[u] = stack[top]] = u;
        } else {
          par[lef[u] = stack[top]] = u;
          rig[par[u] = stack[top - 1]] = u;
        }
        stack[top] = u;
      } else {
        rig[par[u] = stack[top]] = u;
        stack[++top] = u;
      }
    }
  }
}


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[i .. N] ~ P[0 .. i];
    break;
  }
  auto ct = new MaxCartesianTree;
  ct.build(P);
  int dfs(int u) {
    if (!~u) return 0;
    const resL = dfs(ct.lef[u]);
    const resR = dfs(ct.rig[u]);
    return (S[P[u]] == 'W') ? (resL + resR) : max(1, resL, resR);
  }
  const ans = max(1, dfs(ct.rig[0]));
  return ans;
}

void main() {
  /*
  debug {{
    foreach (N; 1 .. 8 + 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);
        foreach (p; 1 << (N-1) .. 1 << N) assert(~dp[p]);
        
        foreach (p; 0 .. 1 << N) {
          string S;
          foreach (u; 0 .. N) S ~= "WB"[p >> u & 1];
          const slv = solve(N, P.dup, S);
          assert(dp[p] == slv, format("%s %s %s: %s %s", N, P, S, dp[p], slv));
        }
      } 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) {
  }
}