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

#include<atcoder/all>
using namespace atcoder;
using mint=atcoder::modint998244353;

#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

#define rep(i,n) for(int i=0;i<(n);i++)
#define rng(i,l,r) for(int i=(l);i<(r);i++)
#define rrep(i,n) for(int i=(n)-1;i>=0;i--)
#define rrng(i,l,r) for(int i=(r)-1;i>=(l);i--)
#define ALL(x) (x).begin(),(x).end()

#define int long long
#define fi first
#define se second

struct fast_io{fast_io(){cin.tie(nullptr)->sync_with_stdio(false);}}_;

signed main(){
	int N,M;cin>>N>>M;
	vector<pair<int,int>> v(N);
	for(auto&&[c,d]:v)cin>>c>>d;
	sort(ALL(v));reverse(ALL(v));

	vector<int> vs={M};
	while(vs.back()>1)vs.push_back(vs.back()/2);
	vector<int> sm={0};for(auto&&e:vs)sm.push_back(sm.back()+e+1);

	int ans=0;

	vector<int> dp(sm.back());
	for(auto&&[c,d]:v){
		if(c==0){
			ans+=d;continue;
		}
		rrep(i,vs.size()){
			rep(j,vs[i]+1){
				if(j-c<0)continue;
				dp[sm[i+1]+(j-c)/2]=max(dp[sm[i+1]+(j-c)/2],dp[sm[i]+j]+d);
			}
		}
	}

	ans+=*max_element(ALL(dp));

	cout<<ans<<endl;
}