#include <iostream>
#include <limits.h>
#include <vector>
#include <algorithm>
#include <unordered_map>
#include <map>
#include <stack>
#include <cmath>
#include <string>
#include <fstream>

#define ll long long

using namespace std;

ifstream fin("energii.in");
ofstream fout("energii.out");

const int inf = 1e8;

int main()
{
    int g, w;
    fin >> g >> w;

    vector<int> putere(g);
    vector<int> cost(g);
    for (int i = 0; i < g; i++)
    {
        fin >> putere[i] >> cost[i];
    }

    // dp[i][j] = costul minim pentru a genera j cantitati de energie, folosind  primele i generatoare
    vector<vector<int>> dp(g + 1, vector<int>(w + 1, inf));

    dp[0][0] = 0;
    for (int i = 1; i <= g; i++)
    {
        for (int j = 0; j <= w; j++)
        {
            dp[i][j] = dp[i - 1][j];
            if (j >= putere[i - 1])
                dp[i][j] = min(dp[i][j], dp[i - 1][j - putere[i - 1]] + cost[i - 1]);
            else
                dp[i][j] = min(dp[i][j], cost[i - 1]);
        }
    }

    if (dp[g][w] == inf)
    {
        fout << -1;
    }
    else
    {
        fout << dp[g][w];
    }

    return 0;
}