#include <fstream>
#define Wmax 5002
#define Gmax 1001
#define inf (1 << 30)
using namespace std;

ifstream f ("energii.in");
ofstream g ("energii.out");

int G, w, e, c;
int P[ Gmax ], C[ Gmax ], v[ Wmax ];

int main()
{
    f >> G >> w;

    for ( int i = 0; i <= w; ++ i )
        v[ i ] = inf;

    for ( int i = 1; i <= G; ++ i )
        f >> P[ i ] >> C[ i ];

    for ( int i = 1; i <= G; ++ i )
    {
        for ( int j = w; j >= 1; -- j )
        {
            if( P[ i ] >= j )
                v[ j ] = min( v[ j ], C[ i ] );
            else if ( v[ j - P[ i ] ] != inf )
                v[ j ] = min( v[ j ], v[ j - P[ i ] ] + C[ i ] );
        }
    }

    g << ( v[ w ] != inf ? v[ w ] : -1 );
    return 0;
}