n <- 100
k <- 2
# n!の計算
a <- 1
for (i in 1 : n) {
  a <- a * i
}
# k!の計算
b <- 1
for (i in 1 : k) {
  b <- b * i
}
# (n-k)!の計算
c <- 1
for (i in 1 : (n-k)) {
  c <- c * i
}
# n!/(k!*(n-k)!)の出力
print(a / (b * c))