2747번 '피보나치 수'

let input = Int(readLine()!)!
var temp = 0
var first = 1
var second = 1
var count = 2
if(input == 1){
    print("1")
}
else if(input == 2){
    print("1")
}
else{
    while(input != count){
        temp = first + second
        first = second
        second = temp
        count += 1
    }
    print(temp)
 
}