Given $A\in\Z^{m\times n}$ and $b\in\Z^m$, we consider the
integer program $\max \{c’x\vert Ax=b;x\in\N^n\}$
and provide an {\it equivalent} and {\it explicit} linear program
$\max \{\widehat{\xcc}’q\vert \m q=r;q\geq 0\}$, where
$\m,r,\widehat{c}$ are easily obtained from $A,b,c$ with no calculation.
We also provide an explicit algebraic characterization
of the integer hull of the convex polytope $\p=\{x\in\R^n\vert
Ax=b;x\geq0\}$. All strong valid inequalities can be obtained from the
generators of a convex cone whose definition is explicit in terms of
$\m$.