Climbing Stairs

public class Solution {
public int climbStairs(int n) {
if (n <= 1) {
return 1;
}
int penultimate = 1, antepenultimate = 1;
int last = 0;
for (int i = 2; i <= n; i++) {
last = penultimate + antepenultimate;
antepenultimate = penultimate;
penultimate = last;
}
return last;
}
}