Given an integer matrix A satisfying certain regularity assumptions, we
consider for a positive integer s the set F_s(A) of all integer vectors b such
that the associated knapsack polytope P(A,b)={x: Ax=b, x non-negative} contains
at least s integer points. In this paper we investigate the structure of the
set F_s(A) sing the concept of s-covering radius. In particular, in a special
case we prove an optimal lower bound for the s-Frobenius number
