function that returns ( n + 1 ) th Fibonacci number Or number of ways to represent n as sum of 1 ' s ▁ ▁ 2' s
int countWays ( int n ) { int F [ 2 ] [ 2 ] = { { 1 , 1 } , { 1 , 0 } } ; if ( n == 0 ) return 0 ; power ( F , n ) ; return F [ 0 ] [ 0 ] ; }