We haven't had performance issues from too many calls to rfind.
CHCYZOGASVETSOEWDBRA5I2JPGZECEVMCMB4QEO7ZLGILL6YYYJAC
LGUCXZFBWCFTVWTSYFITTPTACGPKDZXFO777DUPIPS6GBPZKTLIQC
7PZ4CQFVYUMSJKVCNM75VKK5JCUYU6ICHWPZXXIC3S63YJVFCP5QC
LXTTOB33N2HCUZFIUDRQGGBVHK2HODRG4NBLH6RXRQZDCHF27BSAC
print('rfind')