PER CURIAM. Javier Gallegos challenges the sentence imposed by the District Court after he entered into a plea agreement and pleaded guilty to conspiring to distribute a mixture containing fifty or more grams of methamphetamine. See 21 U.S.C. §§ 841(a)(1), 841(b)(1)(B), 846 (2000). The District Court sentenced Gallegos to sixty months of imprisonment, which was referred to in the plea agreement and is the statutory minimum sentence, and five years of supervised release. Counsel has moved to withdraw on appeal pursuant to Anders v.
California, 386 U.S. 738, 87 S.Ct. 1396, 18 L.Ed.2d 493 (1967), and has filed a brief arguing that the sentence should have been only fifty-one months of imprisonment and is excessive. Gallegos has not filed a pro se supplemental brief. Having thoroughly reviewed the record, we conclude that in the written plea agreement, Gallegos knowingly and voluntarily waived the right to challenge his sentence on appeal. See United States v. Morrison, 171 F.3d 567, 568 (8th Cir.1999). To the extent required, given the appeal waiver, we have further reviewed the record independently under Penson v.
Ohio, 488 U.S. 75, 109 S.Ct. 346, 102 L.Ed.2d 300 (1988), and we find that there are no nonfrivolous issues. Accordingly, we affirm. We also grant counsel’s motion to withdraw. . The Honorable Gary A. Fenner, United States District Judge for the Western District of Missouri.