```
func climbStairs(n int) int {
if n == 0 {return 0}
if n == 1 { return 1}
var a uint32 =1
var b uint32 =1
var ret uint32 = 0
for i:=2; i <=n; i++ {
ret = a + b
b = a
a = ret
}
return int(ret)
}
```