Submission #7254645

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Source Code Expand

#include <bits/stdc++.h>
using namespace std;;
#define ll long long
#define rep(i, n) for(int i = 0;i < n;i++)
#define repr(i, n) for(int i = n;i >= 0;i--)
#define FOR(i, m, n) for(int i = m;i < n;i++)
#define FORR(i, m, n) for(int i = m;i >= n;i--)
#define INF 1<<30
#define LINF 1LL<<62
#define all(x) (x).begin(), (x).end()
#define mp make_pair
#define pb push_back
const int MOD = 1000000007;
 
typedef pair<ll, ll> P;
typedef pair<ll, P> PP;


int main(){
  ios::sync_with_stdio(false);
  cin.tie(0);
  ll n;cin >> n;
  cout << n * (n-1) / 2 << endl;
}

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