#include <iostream>
using namespace std;
using ll = int64_t;
int main() {
// your code goes here
int n;
cin >> n;
ll ans=0;
for(int i=1;i<n;i++){
for(int j=i+1;j<2*i;j++){
if(n-i-j>=2*i){
ans--;
}
if(n-i-j<=j){
break;
}
ans++;
}
}
cout << ans << endl;
return 0;
}
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