#include<bits/stdc++.h>
using namespace std;
int main(int argc, char const *argv[])
{
int n;
cin>>n;
int count = 0;
int arr[n][2];
map<int,int>m;
for (int i = 0; i < n; ++i)
{
/* code */
/* code */
cin>>arr[i][0]>>arr[i][1];
if(m.find(arr[i][0]) != m.end()){
m[arr[i][0]] += 1;
}
else
m[arr[i][0]] = 1;
if(m.find(arr[i][1]) != m.end()){
m[arr[i][1]] += 1;
}
else
m[arr[i][1]] = 1;
count++;
}
int d;
cin>>d;
for (int i = 0; i < n ; ++i)
{
/* code */
//cout<<m[arr[i][0]]<<" "<<m[arr[i][1]]<<"\n";
if (m[arr[i][0]] > 2 || m[arr[i][1]] > 2)
count--;
}
cout<<count<<"\n";
return 0;
}
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