#include <bits/stdc++.h>

using namespace std;

struct pizza{
    int p;
    int d;
};

int main(){
    int n, k;
    cin >> n >> k;
    vector<pizza> v(n);
    for(int i = 0; i < n; i++){
        cin >> v[i].p >> v[i].d;
    }
    sort(v.begin(), v.end(), [](pizza &l, pizza &r){
        return l.p > r.p;
    });

    assert(n < 30);
    int ans = 0;
    for(int i = 0; i < (1 << n); i++){
        int deli = 0;
        int price = 0;
        int count = 0;
        for(int j = 0; j < n; j++){
            if(i & (1 << j)){
                count++;
                if(count & 1) price += v[j].p;
                deli += v[j].d;
            }
        }
        if(price <= k) ans = max(ans, deli);
    }
    cout << ans << endl;
}