RosettaCodeData/Task/Fibonacci-sequence/Sinclair-ZX81-BASIC/fibonacci-sequence-2.basic

 10 INPUT N
 20 LET A=0
 30 LET B=1
 40 FOR I=2 TO N
 50 LET C=B
 60 LET B=A+B
 70 LET A=C
 80 NEXT I
 90 PRINT B