global n, fib_1, fib_2, fib, i;
n := read ();
i := 2;
fib_1 := 1;
fib_2 := 1;
fib := 1;
while i < n do
fib := fib_1 + fib_2;
fib_2 := fib_1;
fib_1 := fib;
i := i+1
od;
write (fib)