#include<bits/stdc++.h>

using namespace std;
typedef long long ll;
ll n,k,ans;

ll sum(ll x){
	if(x>n+1)return 2*n-x+1;
	return x-1;
}

int main(){
	cin>>n>>k;
	k=abs(k);
	for(int i=2;i+k<=2*n;i++)ans+=sum(i)*sum(i+k); 
	cout<<ans<<endl;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;

#define int                     long long int
#define ld                      long double
#define pb                      push_back
#define MOD                     1000000007
#define inf                     3e18
#define vi                      vector<int>
#define vld                     vector<ld>
#define pii                     pair<int,int>
#define mii                     map<int,int>
#define fi                      first
#define se                      second
#define fastIO                  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define db(...)                 __f(#__VA_ARGS__, __VA_ARGS__)
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) { cerr << " "<< name << " : " << arg1 <<'\n'; }
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
    const char* comma = strchr(names + 1, ',');
    cerr.write(names, comma - names) << " : " << arg1 << " | "; __f(comma + 1, args...);
}

typedef tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update> pbds; 
		//order_of_key (k) : Number of items strictly smaller than k .
		//find_by_order(k) : K-th element in a set (counting from zero) (returns an iterator)           


void inp_out()
{
	#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
	freopen("debug.txt", "w", stderr);
	#endif
}

int32_t main()
{
	fastIO
	inp_out();
	int n, x; 
	cin >> n >> x; 
	vector < pii > a(n); 
	for(int i = 0; i < n; ++ i)
		cin >> a[i].fi >> a[i].se; 
	x *= 100; 
	int cur = 0; 
	for(int i = 0; i < n; ++ i)
	{
		cur += (a[i].fi * a[i].se); 
		if(cur > x)
		{
			cout << i + 1 << '\n'; 
			return 0; 
		}
	}
	cout <<  - 1; 
	return 0;
}