#include <bits/stdc++.h>
using namespace std;
const long double PI = 3.141592653589793;
const long long MOD = 1000000007;
const long double EPS = 1e-9;
const long long MAX = LLONG_MAX;
const long long MIN = LLONG_MIN;
const int N = 2e5 + 7;
long long power(long long base, unsigned long long exp, const long long MOD) {
  long long res = 1;
  base %= MOD;
  while (exp) {
    if (exp & 1) {
      res = (res * base) % MOD;
    }
    exp >>= 1;
    base = (base * base) % MOD;
  }
  return res;
}
inline long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }
bool palin(const string& s) {
  long long i = 0, j = s.length() - 1;
  while (i <= j) {
    if (s[i] != s[j]) return false;
    ++i;
    --j;
  }
  return true;
}
long long modinv(long long a, const long long MOD) {
  if (MOD == 1) {
    return 0;
  }
  long long x = 1, y = 0, m = MOD;
  while (a > 1) {
    long long q = a / m, t = m;
    m = a % m;
    a = t;
    t = y;
    y = x - q * y;
    x = t;
  }
  if (x < 0) {
    x += MOD;
  }
  return x;
}
template <typename T>
void input(vector<T>& v) {
  for (int i = 0; i < v.size(); ++i) {
    cin >> v[i];
  }
}
template <typename T>
void printarr(vector<T>& v) {
  for (int x : v) {
    cout << x << " ";
  }
  cout << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n, x, ans = 0, next = 1;
  bool queue = false;
  string s;
  stack<int> st;
  cin >> n;
  for (int i = 0; i < 2 * n; ++i) {
    cin >> s;
    if (s == "add") {
      cin >> x;
      st.push(x);
    } else {
      if (!st.empty()) {
        if (st.top() == next) {
          st.pop();
        } else {
          ++ans;
          st = stack<int>();
        }
      }
      ++next;
    }
  }
  cout << ans << endl;
  return 0;
}
