821C - Okabe and Boxes - CodeForces Solution

// Lakshay's code
#include <bits/stdc++.h>
#define int long long
#define ll long long
#define ull unsigned long long
#define  FOR(i,n) for(long long i = 0; i < (n); i++)
#define  FOR1(i,n) for(long long i = 1; i <= (n); i++)
#define  FOR2(i,n) for(long long i = 2; i <= (n); i++)
#define pb push_back
#define V vector<int>
#define VV vector<V>
#define VVV vector<VV>
#define el cout<<endl;
#define fi first
#define se second
#define noo cout<<"NO"<<endl;
#define yess cout<<"YES"<<endl;
#define se second
#define allv v.begin(),v.end()
// #define sort(v) sort(v.begin(),v.end())
#define fast ios::sync_with_stdio(0);cin.tie(0);cout.tie(0); 
#define w(T) 	ll T; cin>>T; while(T--)

using namespace std;
int n,k;
int32_t main() {
    fast

    cin>>n;
    stack<int> st;
    int cnt=0,r=0;
    FOR(i,2*n){
        string s; cin>>s;
        if(s=="add"){
            int x; cin>>x; st.push(x);
        }
        else{
            r++;
            // if(r==st.top()) st.pop();
            if(st.empty()) continue;
            else{
                if(r==st.top()) st.pop();
                else{
                cnt++;
                while (!st.empty()){
                    st.pop();
                }
                }
            }
        }
        // cout<<cnt<<endl;
    }
    cout<<cnt<<endl;
      

	return 0;
}