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In this paper, we use dynamic programming strategy to find an optimal solution to the EMD (exploiting modification direction) embedding method proposed by Zhang et al. to carry (2n+1)-ary secret digits. An embedding/extraction function defined as a weighted sum function modulo (2n+1) is put forward in the EMD embedding method for secret digit embedding/extraction to/from an image. Among all the different permutations of these (2n+1) numbers, there exists an optimal solution corresponding to an embedding/extraction function, which can be used to minimize the distortion of stego-image. Without doubt, finding the best permutation will take a lot of computational time. Therefore, we shall use dynamic programming strategy to get an optimal solution.