fL <- "student2017.txt"
dta <- read.table(fL, h = T)
dta$ID <- as.character(dta$ID)
miss <- "U76067010"
dta2 <- data.frame(c(dta[1:13, ], miss, dta[14:16, ]))
names(dta2) <- "ID";dta2                 

##           ID
## 1  D84057058
## 2  C44035023
## 3  D84041162
## 4  D84046081
## 5  D84021057
## 6  U36037025
## 7  U36041074
## 8  U36041090
## 9  U36051087
## 10 U36031118
## 11 U36041082
## 12 U76051019
## 13 U76054025
## 14 U76067010
## 15 U76064062
## 16 U76041064
## 17 U76041080