#pragma GCC optimize("Ofast,unroll-loops,O3")
#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
#include "algo/debug.h"
#else
#define debug(...) 73
#endif
using int64 = int64_t;
using ld = long double;
using uint64 = uint64_t;
using int128 = __int128_t;
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
const int md = 1e9 + 7;
const int64 inf = 1e18;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
int n, k;
cin >> n >> k;
for (int i = 0; i < n; i++) {
int x, y;
cin >> x >> y;
}
int sum = 0;
for (int i = 1; i <= n; i++) {
if (sum + i > k) {
sum = 0;
}
sum += i;
}
cout << sum << '\n';
return 0;
}
