ruby, 36 bytes

Result

AC

Duration

697ms

Code [DL]

$><<gets.gsub(/(.)(\d)/){$1*$2.to_i}

stdin

x7a4oc7z3e2bign5y9j4bf7w5v6z5c9l6a5a8n8t8g8d4y6o7z7m8h2y5e4r3x8f5m4q6j9f2e9o5p5g4l2k8a3u7b9s9t7

stdout

xxxxxxxaaaaoccccccczzzeebignnnnnyyyyyyyyyjjjjbfffffffwwwwwvvvvvvzzzzzcccccccccllllllaaaaaaaaaaaaannnnnnnnttttttttggggggggddddyyyyyyooooooozzzzzzzmmmmmmmmhhyyyyyeeeerrrxxxxxxxxfffffmmmmqqqqqqjjjjjjjjjffeeeeeeeeeooooopppppggggllkkkkkkkkaaauuuuuuubbbbbbbbbsssssssssttttttt

stderr

strace