On a coordinate plane, a graph shows age in months on the x-axis and shoe size on the y-axis. A step graph has horizontal segments that are each 1 unit long. The left end of each segment is an open circle. The right end of each segment is a closed circle. The left-most segment goes from (0, 0) to (3, 0). Each segment is 1 unit higher and 1 unit farther to the right than the previous segment. The rightmost segment goes from (12, 4) to (15, 4). The graph shows the average shoe size for a baby or toddler as a function of age in months. What shoe size would be recommended for a four-month-old baby?
Shoe size: