var n, fib_1 = 1, fib_2 = 1, fib = 1;
n := read ();

for var i; i := 2, i < n, i := i+1
do
      fib   := fib_1 + fib_2;
      fib_2 := fib_1;
      fib_1 := fib
od;

write (fib)