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# 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.

**Example 1:**

```
Input: 2
Output: 2
Explanation: There are two ways to climb to the top.
1. 1 step + 1 step
2. 2 steps
```

**Example 2:**

```
Input: 3
Output: 3
Explanation: There are three ways to climb to the top.
1. 1 step + 1 step + 1 step
2. 1 step + 2 steps
3. 2 steps + 1 step
```

```java
class Solution {
    public int climbStairs(int n) {
        if (n == 1)
            return 1;
        else if (n == 2)
            return 2;
        else if (n == 3)
            return 3;
        int dp2 = 2, dp3 = 3;
        for (int i = 4; i <= n; i++) {
            int dpN = dp2 + dp3;
            dp2 = dp3;
            dp3 = dpN;
        }
        return dp3;
    }
}
```