else-if returns unexpected '<='

Can someone tell me whats wrong with my R code:

       for (i in 1:6)
    {
      probability_of_x[i] = i/21
    }
    U = runif(1,0,1)
    
    if(U<=probability_of_x[1]){
  X=1
  print("X = 1")
  }else if(probability_of_x[1]<U<=probability_of_x[2]){
  X=2
  print("X = 2")
  } else if(probability_of_x[2]<U<=probability_of_x[3]){
  X=4
  print("X = 3")
  } else if(probability_of_x[3]<U<=probability_of_x[4]){
  X=4
  print("X = 4")
  } else if(probability_of_x[4]<U<=probability_of_x[5]){
  X=5
  print("X = 5")
  } else(probability_of_x[5]<U<=probability_of_x[6]){
  X=6
  print("X = 6")}

I get the error:

Error: unexpected '<=' in: " print("X = 1") }else if(probability_of_x[1]<U<="