#include <bits/stdc++.h>
#define oo 9999999 
using namespace std;
ifstream f("energii.in");
ofstream g("energii.out");
int G, W;
int e[1005], c[1005];
int dp[5005];
int minim = oo;

void Read()
{
  f>>G>>W;
  for(int i = 1;i <= G;++i)
    f>>e[i]>>c[i];
  memset(dp, oo, sizeof(dp));
  dp[0] = 0;
  for(int i = 1;i <= G;++i)
    for(int j = W;j >= 0;--j)
      if(j + e[i] >= W)
        minim = min(minim, dp[j] + c[i]);
      else if(dp[j + e[i]] > dp[j] + c[i])
        dp[j + e[i]] = dp[j] + c[i];
  if(minim == oo)
    g<<-1;
  else
    g<<minim;
}

int main()
{
  Read();
  return 0;
}