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

typedef long long ll;

#define deb(...) logger(#__VA_ARGS__, __VA_ARGS__)
template<typename ...Args>
void logger(string vars, Args&&... values) {
  cout << vars << " = ";
  string delim = "";
  (..., (cout << delim << values, delim = ", "));
  cout << '\n';
}

using ld = long double;

void solve() {
  int n;
  string s;
  cin >> n >> s;
  auto check = [&] (int g) {
    ll all = 0;
    vector<int> pos;
    for (int i = 0; i < 2 * n - 1; ++i) {
      if (s[i] == 'W') pos.push_back(i);
      if (pos.size() < g) continue;
      int l = pos.size() - g;
      if (i - n + 1 <= (l ? pos[l - 1] : -n*3)) continue;
      assert(l >= 0);
      all += (pos[l] - (l ? pos[l - 1] : 0));
    }
    
    return all >= n;
  };
  int l = 1, r = n * 2 - 1, best = 0;
  while (l <= r) {
    int m = (l + r) / 2;
    if (check(m)) {
      best = m;
      l = m + 1;
    } else r = m - 1; 
  }
  cout << best << '\n';
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int t = 1;
  // cin >> t;
  while(t--) {
    solve();
  }
}