#include <bits/stdc++.h>
using namespace std;
int main() {
// your code goes here
int n;
cin>>n;
int t=2*n,fl=0;
stack<int>st;
int ex=1,ans=0;
while(t--)
{
string s;
int el;
cin>>s;
if(s[0]=='a')
{
cin>>el;
if(el==1 && t==2*n-1){
ex=1;
fl=0;
}
else if(el==n && t==2*n-1){
ex=n;
fl=1;
}
st.push(el);
}
else{
int ex1=st.top();
if(ex==ex1)
ans++;
st.pop();
if(fl==0)
ex++;
else
ex--;
}
}
cout<<ans;
return 0;
}
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