#include<iostream>
#include<fstream>
#define inf 2e8
using namespace std;
int e[1012],cost[1012],cmin=-1;
int a[2][5013],C;
int main(void)
{
int n,c;
fstream f,g;
f.open("energii.in",ios::in);
g.open("energii.out",ios::out);
f>>n>>C;
int i,maxim=-1;
for(i=1;i<=n;i++)
{
f>>e[i]>>cost[i];
}
int j;
for (i=0;i<=1;i++)
for (j=1;j<=5012;j++)
a[i][j]=inf;
for (i=1;i<=n;i++)
if (i%2==1)
for (c=1;c<=C;c++)
{
if (e[i]<=c)
a[1][c]=min(a[0][c],a[0][c-e[i]]+cost[i]);
else
a[1][c]=min(a[0][c],cost[i]);
}
else       
for (c=1;c<=C;c++)
{
if (e[i]<=c)
a[0][c]=min(a[1][c],a[1][c-e[i]]+cost[i]);
else
a[0][c]=min(a[1][c],cost[i]);
}
if (a[n%2][C]!=inf)
g<<a[n%2][C];
else
g<<-1;
}