#include <bits/stdc++.h>
class big_integer {
 public:
  big_integer(int32_t v) {
    if (v >= base) {
      data_.push_back(v % base);
      data_.push_back(v / base);
    } else {
      data_.push_back(v);
    }
  }
  void inc() {
    int32_t carry = 1;
    size_t ptr = 0;
    while (carry != 0 && ptr < data_.size()) {
      data_[ptr] += 1;
      if (data_[ptr] == base) {
        data_[ptr] -= base;
      } else {
        carry = 0;
      }
      ptr += 1;
    }
    if (carry != 0) {
      data_.push_back(carry);
    }
  }
  void mult2() {
    int32_t carry = 0;
    for (size_t i = 0; i < data_.size(); ++i) {
      data_[i] = data_[i] * 2 + carry;
      if (data_[i] >= base) {
        data_[i] -= base;
        carry = 1;
      } else {
        carry = 0;
      }
    }
    if (carry != 0) {
      data_.push_back(carry);
    }
  }
  void print(std::ostream& os) const {
    os << data_.back();
    for (size_t i = data_.size() - 2; i < data_.size(); --i) {
      os << std::setw(9) << std::setfill('0') << data_[i];
    }
  }

 private:
  std::vector<int32_t> data_;
  static const int32_t base = 1000000000;
  big_integer() {}
};
struct operation {
  std::string op;
  int32_t x;
};
std::istream& operator>>(std::istream& is, operation& o) {
  return is >> o.op >> o.x;
}
int main() {
  std::ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  size_t n;
  std::cin >> n;
  std::vector<operation> ops(n);
  std::vector<size_t> poss(2001, n);
  for (size_t i = 0; i < n; ++i) {
    std::cin >> ops[i];
    if (ops[i].op == "sell") {
      poss[ops[i].x] = i;
    }
  }
  std::vector<int32_t> used(n);
  big_integer result(0);
  for (int32_t i = 2000; i >= 0; --i) {
    result.mult2();
    if (poss[i] == n) {
      continue;
    }
    size_t pos = poss[i];
    while (pos < n) {
      if (used[pos] || (ops[pos].op == "win" && ops[pos].x == i)) {
        break;
      }
      pos -= 1;
    }
    if (pos < n && !used[pos]) {
      for (size_t j = pos; j <= poss[i]; ++j) {
        used[j] = 1;
      }
      result.inc();
    }
  }
  result.print(std::cout);
  std::cout << '\n';
}
