70. Climbing Stairs

You are climbing a stair case. It takes n steps to reach to the top.
Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
Note: Given n will be a positive integer.

public class Solution {
    public int climbStairs(int n) {
        if(n==0)
          return 0;
        if(n==1)
          return 1;
        if(n==2)
          return 2;
        int f1 = 1,f2 = 2;
        int f = f1 + f2;
        for(int i=3;i<=n;i++)
        {
            f = f1 + f2;
            f1 = f2;
            f2 = f;
        }
        return f;
    }
}