ReadTableFixCol

library(data.table)
library(magrittr)

dt <- fread("11   22   33   44   55   66
11   22   33   44   55   66  77  88  99
11   22   33   44   55   66  77  88  99  00", fill = TRUE)

dt %>% .[, ':='(V11 = NA, V12 = NA)]

dt <- rbind(dt %>% .[, c(paste0("V", 1:6))] %>% .[, I := .I * 2 -1],
            dt %>% .[, c(paste0("V", 7:12))] %>% .[, I := .I * 2] %>% setnames(colnames(.), c(paste0("V", 1:6), "I"))) %>%
    setorder(I) %>% .[, I := NULL] %>%
    .[rowSums(is.na(.)) != ncol(.), ]

dt