#include<bits/stdc++.h>
using namespace std;
using ll = long long;
pair<int, int> a[10010];
ll dp[10000010];
void solve() {
    int n, m;
    cin >> n >> m;
    for (int i = 1;i <= n;i++) {
        cin >> a[i].first >> a[i].second;
    }
    sort(a + 1, a + 1 + n);
    memset(dp, 0, sizeof dp);
    for (int i = 1;i <= n;i++) {
        for (int j = m;j >= a[i].first;j--) {
            dp[j] = max(dp[j], dp[(j - a[i].first) / 2] + a[i].second);
        }
    }
    cout << dp[m] << '\n';
}

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);
    int q=1;
    //cin >> q;
    while (q--) {
        solve();
    }
    return 0;
}