#include<bits/stdc++.h>
using namespace std;
ifstream F("energii.in");
ofstream G("energii.out");
short n,m,i,j,e,c,s[5001],r[5001];
int main()
{
	F>>n>>m;
	for(j=0;j<n;++j) {
		F>>e>>c;
      	for(i=1;i<=m;++i)
            s[i]=(!j?(i<=e?c:10001):(r[i]<c+(i>e?r[i-e]:0)?r[i]:(c+(i>e?r[i-e]:0))));
        for(i=1;i<=m;++i)
            r[i]=s[i];
	}
    G<<(s[m]!=10001?s[m]:-1);
    return 0;
}