#include <bits/stdc++.h>
#define ll long long
#define pb push_back
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
#define sz(x) (int)x.size()
#define fi first
#define sd second
#define all(x) x.begin(), x.end()
//#pragma GCC target ("avx2")
//#pragma GCC optimization ("O3")
//#pragma GCC optimization ("unroll-loops")
using namespace std;
//using namespace __gnu_pbds;
//typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> ordered_set;
int main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int n;
cin >> n;
string s;
cin >> s;
ll skok = n;
cout << skok * (skok - 1) / 2ll;
}
