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

#define ll long long

int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0), cout.tie(0);

    int n; cin >> n; n *= 2;

    set<int> ord;
    vector<int> v;
    int cnt = 0;

    while(n--)
    {
        string req; int a; cin >> req;
        if(req == "add")
        {
            int a; cin >> a;
            v.push_back(a);
        }
        else
        {
            if(!v.empty())
            {
                if(v.back() == a)
                    v.pop_back();
                else
                {
                    while(!v.empty())
                    {
                        ord.insert(v.back());
                        v.pop_back();
                    }
                    cnt++;
                    ord.erase(ord.begin());
                }
            }
            else ord.erase(ord.begin());
        }
    }
    cout << cnt;

//3
//add 1
//remove
//add 2
//add 3
//remove
//remove
}