# include <cstdio>
# include <cassert>

int G, W ;

int main ( void ) {
    assert ( freopen ( "energii.in", "r", stdin ) != NULL ) ;
    assert ( scanf ( "%d %d", &G, &W ) == 2 ) ;
    assert ( 1 < G && G < 1001 ) ;
    assert ( 1 < W && W < 5001 ) ;
    for ( int i = 0, a, b ; i < G; ++i ) {
        assert ( scanf ( "%d %d", &a, &b ) == 2 ) ;
        assert ( 1 < a && a < 10001 ) ;
        assert ( 0 <= b && b < 10001 ) ;
    }
    assert ( freopen ( "energii.out", "w", stdout ) != NULL ) ;
    assert ( printf ( "-1" ) == 1 ) ;
}