Full question:

Given N step stair, how many number of ways can you climb if you use either 1 or 2 at a time?

It will be F(n+1) fibonacci number, there Fibonacci numbers are defined by the recurrence relation:

F(n) = F(n-2) + F(n-1)

for N stair number of ways will be

N=1 => 1 = F(2)

N=2 => 2 = F(3)

N=3 => 3 = F(4)

N=4 => 5 = F(5)

N=5 => 8 = F(6)

N=6 => 13 = F(7)

....

Fibonacci numbers on Wikipedia

Given N step stair, how many number of ways can you climb if you use either 1 or 2 at a time?

**Answer**It will be F(n+1) fibonacci number, there Fibonacci numbers are defined by the recurrence relation:

F(n) = F(n-2) + F(n-1)

for N stair number of ways will be

N=1 => 1 = F(2)

N=2 => 2 = F(3)

N=3 => 3 = F(4)

N=4 => 5 = F(5)

N=5 => 8 = F(6)

N=6 => 13 = F(7)

....

N=k => F(k+1)

Fibonacci numbers on Wikipedia