#include <bits/stdc++.h> // ver2.3.8
//#include <boost/math/tools/minima.hpp>
//#include <boost/multiprecision/cpp_int.hpp>
#define fmin brent_find_minima
#define int long long
#define endl "\n"
#define ALL(v) (v).begin(),(v).end()
#define COUNT(a,k) upper_bound(ALL(a),k)-lower_bound(ALL(a),k)
#define BIGGER(a,k) a.end()-upper_bound(ALL(a),k)
#define SMALLER(a,k) lower_bound(ALL(a),k)-a.begin()
#define Vi vector<int>
#define VVi vector<Vi>
#define Vs vector<string>
#define Pii pair<int,int>
#define VPii vector<Pii>
#define Tiii tuple<int,int,int>
#define VTiii vector<Tiii>
#define PQi priority_queue<int>
#define PQir priority_queue<int,vector<int>,greater<int>>
#define pb push_back
#define mp make_pair
#define mt make_tuple
#define itos to_string
#define stoi stoll
#define FI first
#define SE second
#define cYES cout<<"YES"<<endl
#define cNO cout<<"NO"<<endl
#define cYes cout<<"Yes"<<endl
#define cNo cout<<"No"<<endl
#define cyes cout<<"yes"<<endl
#define cno cout<<"no"<<endl
#define sortr(v) sort(v,greater<>())
#define rep(i,a,b) for(int i=a;i<b;i++)
#define repeq(i,a,b) for(int i=a;i<=b;i++)
#define repreq(i,a,b) for(int i=a;i>=b;i--)
#define leng(n) (int)(log10(n)+1)
#define dem(a,b) ((a+b-1)/(b))
#define Vin(a) rep(iI,0,a.size())cin>>a[iI]
#define INF 3000000000000000000  //  3.0*10^18(MAXの1/3くらい)
#define MAX LLONG_MAX
#define PI 3.141592653589793238462
#define MOD 1000000007  //  10^9 + 7

using namespace std;
/* fmin(f,L,R,100) で関数の最小値を(x,min)で返す　*/
//using boost::math::tools::brent_find_minima;
/* cpp_int (任意の長さのint) */
//using boost::multiprecision::cpp_int;

/* デバッグ用 */
void Vout(auto a){if(a.size()==0) cout<<"."<<endl;
else{rep(i,0,a.size()-1)cout<<a[i]<<' ';if(a.size()>0)cout<<a.back()<<endl;}return;}
void Verr(auto a){if(a.size()==0) cerr<<"."<<endl;
else{rep(i,0,a.size()-1)cerr<<a[i]<<' ';if(a.size()>0)cerr<<a.back()<<endl;}return;}
void VVout(auto a){if(a.size()==0)cout<<"."<<endl;
else{rep(i,0,a.size())Vout(a[i]);}return;}
void VVerr(auto a){if(a.size()==0)cerr<<"."<<endl;
else{rep(i,0,a.size())Verr(a[i]);}return;}
void VPout(auto a){if(a.size()==0)cout<<"."<<endl;
else{rep(i,0,a.size())cout<<a[i].FI<<' '<<a[i].SE<<endl;}return;}
void VPerr(auto a){if(a.size()==0)cerr<<"."<<endl;
else{rep(i,0,a.size())cerr<<a[i].FI<<' '<<a[i].SE<<endl;}return;}

/* 便利関数 */
int gcd(int a,int b){return b?gcd(b,a%b):a;} // 最大公約数gcd
int lcm(int a,int b){return a/gcd(a,b)*b;} // 最小公倍数lcm
int mypow(int x, int n, int m){ // 累乗x^n(mod m) O(log(n))
if(n==0)return 1;if(n%2==0)return mypow(x*x%m,n/2,m);else return x*mypow(x,n-1,m)%m;}
int scomb(int n, int r){if((n-r)<r)r=n-r; // nCr(小さい場合)
int a=1;for(int i=n;i>n-r;--i){a=a*i;}for(int i=1;i<r+1;++i){a=a/i;}return a;}
int comb(int n, int r){if((n-r)<r)r=n-r; // nCr(%MOD)
int a=1;for(int i=n;i>n-r;--i){a=a*i%MOD;}for(int i=1;
i<r+1;++i){a=a*mypow(i,MOD-2,MOD)%MOD;}return a%MOD;}
Vi stpowV(){Vi a(100001);
a[0]=1;repeq(i,1,100000)a[i]=a[i-1]*i%MOD;return a;}
//Vi stpow = stpowV(); // 階乗配列(%MOD)
Vi Vsum(Vi &v){Vi S(v.size()+1);rep(i,1,S.size())S[i]+=v[i-1]+S[i-1];return S;}// 累積和
int digit(int k,int i){string s = itos(k);return s[s.size()-i]-'0';} // i桁目の数字
void press(auto &v){v.erase(unique(ALL(v)),v.end());} // 圧縮
Vi zip(Vi b){int Z=b.size(); // 座標圧縮
Pii p[Z+10];int a=b.size();Vi l(a);for(int i=0;i<a;i++)
p[i]=mp(b[i],i);sort(p,p+a);int w=0;for(int i=0;i<a;i++)
{if(i&&p[i].first!=p[i-1].first)w++;l[p[i].second]=w;}return l;}
Vi beki2V(){Vi a(61);int q = 1;rep(i,0,61){a[i]=q;q*=2;}return a;}
Vi beki2 = beki2V(); // 2^n配列
int modiv(int a,int b){return a*mypow(b,MOD-2,MOD)%MOD;} // a÷b(MOD環境)



signed main() {
  cin.tie(0);cout.tie(0);ios::sync_with_stdio(false);cout<<fixed<<setprecision(12);
  int n,k;
 cin >> n >> k;
 Vi w(n),v(n);
 int wmax=0,vmax=0;
 
 rep(i,0,n) {
   cin >> v[i] >> w[i];
   wmax = max(wmax,w[i]);
   vmax = max(vmax,v[i]);
 }
 
 
 if(k <= 200000){ /* kが小さいとき */
   
   VVi dp(n+5,Vi(k+5));
   
   rep(i,0,n){
     repeq(j,0,k){
       
       if(j-w[i] >= 0){
         dp[i+1][j] = max(dp[i][j],dp[i][j-w[i]] + v[i]);
       }
       
       else dp[i+1][j] = dp[i][j];
     }
   }
   cout << dp[n][k] << endl;
   return 0;
 }
 
 else if(vmax <= 2000){ /* vが小さいとき */
   VVi dp(n+5,Vi(100010,INF));
   dp[0][0] = 0;
 
   rep(i,0,n){
     repeq(j,0,100010){
       
       if(j-v[i] >= 0){
         dp[i+1][j] = min(dp[i][j],dp[i][j-v[i]] + w[i]);
       }
       
       else dp[i+1][j] = dp[i][j];
     }
   }
   int ans = 0;
   rep(i,0,100010){
     if(dp[n][i] <= k && dp[n][i] != 0) ans = i;
   }
   cout << ans << endl;
   return 0;
 }
 
 else if(n <= 40){   /* nが小さいとき */
   int m = n/2;
   Vi aw(m),av(m),bw(n-m),bv(n-m);
   
   rep(i,0,n){
     if(i <= m-1) {
       aw[i] = w[i];
       av[i] = v[i];
     }
     else {
       bw[i-m] = w[i];
       bv[i-m] = v[i];
     }
   }
   
   int now,ct = mypow(2,m,MOD);
   Vi ch(m);
   int vs,ws;
   VPii awv,bwv;
   
   rep(i,0,ct){
     now = i;
     vs=0,ws=0;
     rep(j,0,m){
       ch[j] = now%2;
       now /= 2;
     }
     rep(j,0,m){
       if(ch[j]==1) {
         vs += av[j];
         ws += aw[j];
       }
     }
     awv.pb(mp(ws,vs));
   }
   
   ct = mypow(2,n-m,MOD);
   ch = Vi(n-m);
   
   rep(i,0,ct){
     now = i;
     vs=0,ws=0;
     rep(j,0,n-m){
       ch[j] = now%2;
       now /= 2;
     }
     rep(j,0,n-m){
       if(ch[j]==1) {
         vs += bv[j];
         ws += bw[j];
       }
     }
     bwv.pb(mp(ws,vs));
   }
   
   sort(ALL(awv));
   sort(ALL(bwv));
   
   now = -1;
   rep(i,0,awv.size()){
     if(awv[i].SE > now) {
       now = awv[i].SE;
     }
     else {
       awv[i] = mp(0,0);
     }
   }
   now = -1;
   rep(i,0,bwv.size()){
     if(bwv[i].SE > now) {
       now = bwv[i].SE;
     }
     else {
       bwv[i] = mp(0,0);
     }
   }
   
   sort(ALL(awv));
   sort(ALL(bwv));
   
   int ans = 0;
   
   av = Vi(0);
   aw = Vi(0);
   bv = Vi(0);
   bw = Vi(0);
   
   rep(i,0,awv.size()){
     av.pb(awv[i].SE);
     aw.pb(awv[i].FI);
   }
   rep(i,0,bwv.size()){
     bv.pb(bwv[i].SE);
     bw.pb(bwv[i].FI);
   }
   
   int nowv;
   
   rep(i,0,aw.size()){
     now = k-aw[i];
     if(now < 0) break;
     nowv = av[i];
     int qw = SMALLER(bw,now)+COUNT(bw,now);
     qw--;
     nowv += bv[qw];
     ans = max(ans,nowv);
   }
   
   cout << ans << endl;
   return 0;
 }
 else {cout << "impossible" << endl;return 0;}
  return 0;
}



Measured memory_bytes: 82136