/*
ID: Aman Raj
LANG: C++
TASK: prefix
*/
//#include<iostream>
#include <stdio.h>
//#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
#include<math.h>
typedef  long long  ll;
#include <bits/stdc++.h>
#include <vector>
#include <set>
#include <map>
#include <string>
#include <cstdio>
#include <cstdlib>
#include <climits>
#include <utility>
#include <algorithm>
#include <cmath>
#include <queue>
#include <stack>
#include <iomanip>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
//setbase - cout << setbase (16); cout << 100 << endl; Prints 64
//setfill -   cout << setfill ('x') << setw (5); cout << 77 << endl; prints xxx77
//setprecision - cout << setprecision (14) << f << endl; Prints x.xxxx
//cout.precision(x)  cout<<fixed<<val;  // prints x digits after decimal in val

using namespace std;
using namespace __gnu_pbds;

#define f(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) f(i,0,n)
#define fd(i,a,b) for(i=a;i>=b;i--)
#define pb push_back
#define mp make_pair
#define vi vector< int >
#define vl vector< ll >
#define ss second
#define ff first
//#define ll long long
#define pii pair< int,int >
#define pll pair< ll,ll >
#define sz(a) a.size()
#define inf (1000*1000*1000+5)
#define all(a) a.begin(),a.end()
#define tri pair<int,pii>
#define vii vector<pii>
#define vll vector<pll>
#define viii vector<tri>
#define mod (1000*1000*1000+7)
//#define mod 7
#define pqueue priority_queue< int >
#define pdqueue priority_queue< int,vi ,greater< int > >
//#define flush fflush(stdout)
#define primeDEN 727999983
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#include <fstream>
// find_by_order()  // order_of_key
typedef tree<
	int,
	null_type,
	less<int>,
	rb_tree_tag,
	tree_order_statistics_node_update>
	ordered_set;


   bool comp(pair<ll,ll> p1, pair<ll,ll> p2)
   {
    if(p1.first!=p2.first)return p1.first < p2.first;
     else return p1.second < p2.second;
   }

   vector<ll> dpfact;
   ll fact(ll a)
   { return dpfact[a];

   }

   ll power1(ll a, ll b)//a raised to power b
   {  if(b<=0) return 1; if(b==1) return a;
       ll c=power1(a,b/2);
        c*=c;c%=mod;if(b%2==1) c*=a;c%=mod;
        return c;
   }
   ll mi(ll a,ll m)
   { ll c= power1(a,m-2);

     return c;
   }
   ll findpower(ll a,ll b)
   {
       ll i=0;
       ll c=1;
        while(1)
        {
            c*=2;

            if(c>a)return i;
            i++;
        }
   }
  /* vector<vector<ll> > v;
   vector<ll> visited;
   ll ans=0;
   void dfs(ll i)
   { visited[i]=1;
     ans++;
      for(auto x:v[i])
      {
          if(!visited[x])dfs(x);
      }

   }*/
  ll aman(ll a,ll b)
  {
     ll i=1;
      while(1)
      { b*=2;
         if(b>a)return i;
          i++;

      }
  }
  ll power2(ll a,ll b)
  { if(b==0)return 1;
      ll i=1;
       while(i<b)
       {
           a*=2;i++;
       }
       return a;
  }
  ll myXOR(ll x, ll y)
{
    ll res = 0; // Initialize result

    // Assuming 32-bit Integer
    for (int i = 31; i >= 0; i--)
    {
       // Find current bits in x and y
       bool b1 = x & (1 << i);
       bool b2 = y & (1 << i);

        // If both are 1 then 0 else xor is same as OR
        bool xoredBit = (b1 & b2) ? 0 : (b1 | b2);

        // Update result
        res <<= 1;
        res |= xoredBit;
    }
    return res;
}
 ll myAND(ll x, ll y)
{
    ll res = 0; // Initialize result

    // Assuming 32-bit Integer
    for (int i = 31; i >= 0; i--)
    {
       // Find current bits in x and y
       bool b1 = x & (1 << i);
       bool b2 = y & (1 << i);

        // If both are 1 then 0 else xor is same as OR

    if(b1&b2)return 1;
    }
    return 0;
}
   int main()
{    ofstream fout("tcase.txt");
      //cout<<myAND(5,3);
    //ll n;cin>>n;vector<ll> v(n);for(ll i=0;i<n;i++)cin>>v[i];
     /*ll a,b;
      cin>>a>>b;
       ll i=1;
        while(1)
        {
            ll c=a*i-(i-1);
            if(c>=b){ cout<<i;return 0; }
            i++;
        }*/
ll n;cin>>n;cout<<n*(n-1)/2;

    return 0;
 }


Measured memory_bytes: 256