class Solution {
    public int smallestCommonElement(int[][] mat) {
        int[] count = new int[10001];
        
        int n = mat.length, m = mat[0].length;
        for (int j = 0; j < m; ++j)
            for (int i = 0; i < n; ++i)
                if (++count[mat[i][j]] == n)
                    return mat[i][j];
        
        return -1;
    }
}