#include <bits/stdc++.h>
#define f first
#define s second
using namespace std;
ifstream in("energii.in");
ofstream out("energii.out");
pair<int,int> a[1001];
int dp[2][5001];
int main(){
    int n,w,i,j,sum=0;
    bool b=0;
    in>>n>>w;
    for(i=1; i<=n; ++i){
        in>>a[i].f>>a[i].s;
        sum+=a[i].f;
    }
    if(sum<w){
        out<<-1;
        return 0;
    }
    for(i=1; i<=n; ++i, b=!b){
        for(j=1; j<=w; ++j){
            dp[b][j]=dp[!b][j];
            if(j>=a[i].f)
                dp[b][j]=max(dp[b][j], dp[!b][j+a[i].f]+a[i].s);
        }
    }
    out<<dp[!b][w];
    return 0;
}