#include <bits/stdc++.h>
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int s_energie[1001],s_cost[1001];
int main()
{
    int n,i,j,k,minn=10000001;
    f>>n>>k;
    for(i=1;i<=n;i++){
        f>>s_energie[i]>>s_cost[i];
        s_energie[i]+=s_energie[i-1];
        s_cost[i]+=s_cost[i-1];
    }
    for(i=1;i<=n;i++){
        for(j=i;j<=n;j++){
            if(s_energie[j]-s_energie[i-1]>=k)
                if(s_cost[j]-s_cost[i-1]<minn)
                    minn=s_cost[j]-s_cost[i-1];
        }
    }
    if(minn==10000001)
        g<<-1;
    else
    g<<minn<<"\n";
    return 0;
}