The ornamental design for a flag, as shown and described.
FIG. 1 is a front elevational view of a flag shown in a position of use on a flagpole. The broken lines represent environmental subject matter that forms no part of the claim.
FIG. 2 is an enlarged front elevational view of the flag of FIG. 1.
FIG. 3 is a rear elevational view of the flag of FIG. 1 shown in a position of use on a flagpole. The broken lines represent environmental subject matter that forms no part of the claim.
FIG. 4 is a rear elevational view of the flag of FIG. 2.
FIG. 5 is a top plan view of the flag of FIG. 2; and,
FIG. 6 is a right side elevational view of the flag of FIG. 2. The left side elevational view is identical to the right side elevational view.