mystery <- function(x) {
  # We use dnorm(x, mean, sd)
  p1 <- dnorm(x, -5, 0.5)
  p2 <- 0.7 * dnorm(x, 5, 1.5)
  p3 <- 0.5 * dnorm(x, 20, 0.2)
  
  return(p1 + p2 + p3)
}