AMGEN INC. $750,000,000 3.000% SENIOR NOTES DUE 2029 $1,000,000,000 3.350% SENIOR NOTES DUE 2032 $1,000,000,000 4.200% SENIOR NOTES DUE 2052 $1,250,000,000 4.400% SENIOR NOTES DUE 2062 Underwriting Agreement