#include <fstream>

using namespace std;

ifstream fin("energii.in");
ofstream fout("energii.out");
int dp[1005][5005], n, w, cost[1005], e[1005];
int main()
{
    fin >> n >> w;
    int i, j;
    for ( i = 1; i <= n; ++i )
        fin >> e[i] >> cost[i];

    for( i = 0; i <= n; ++i )
        for ( j = 1; j <= w; ++j )
            dp[i][j] = 1e9;

    for ( i = 1; i <= n; ++i )
        for ( j = 1; j <= w; ++j )
        {
            dp[i][j] = min(dp[i - 1][j], dp[i - 1][max(0, j - e[i])] + cost[i] );
            //fout << dp[i][j] <<  " ";
        }

    if ( dp[n][w] == 1e9 )
        fout << -1 << '\n';
    else
        fout << dp[n][w] << '\n';
    return 0;
}