Sum

////////////////////////////////////////////////
//                                            //
//  Author: Muhammad Faishol Amirul Mukminin  //
//                                            //
////////////////////////////////////////////////
#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pi;
typedef pair<pi,int> pii;
typedef pair<ll,ll> pl;
typedef pair<pl,ll> pll;
typedef pair<double,double> pd;
typedef pair<pd,double> pdd;
typedef pair<string, int> psi;
 
#define FOR(i,x,y) for(int i=(x);i<(y);i++)
#define FORN(i,x,y) for(int i=(x);i<=(y);i++)
#define REV(i,a,b) for(int i=(a);i>(b);i--)
#define REVN(i,a,b) for(int i=(a);i>=(b);i--)
#define BTW(i,a,b) a <= i && i <= b
 
#define DB(x) cerr << #x << ": " << x << endl;
 
#define fi first
#define se second
#define PUB push_back
#define POB pop_back
#define PUF push_front
#define POF pop_front
#define ALL(v) (v).begin(),(v).end()
#define endl "\n"
 
const double EPS = 1e-9;
const double PI = acos(-1);
const ll MOD = 1e9+7;
const int INF = 0x7FFFFFFF;
const ll LINF = 0x7FFFFFFFFFFFFFFFLL;
const ull UINF = 0xFFFFFFFFFFFFFFFFLL;
const int dCol[] = {0,+1,0,-1,+1,+1,-1,-1};
const int dRow[] = {-1,0,+1,0,-1,+1,+1,-1};
 
template <typename T>
inline void VIN(vector<T> &i){ T x; cin >> x; i.PUB(x); }
inline void FIO(string i){ freopen((i+".in").c_str(), "r", stdin); freopen((i+".out").c_str(), "w", stdout);}

int N, ans = 0;

int main(){
	ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
	
	cin >> N;
	FORN(i,1,N) FORN(j,i+1,N){
		int K = N-(i+j);
		if(K > 0 && K > j) ans++;
	}
	cout << ans << endl;
	return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED