DO
INPUT "vvedite 1 chislo ", a
IF a <= 0 THEN PRINT "nevernyj vvod"
LOOP UNTIL a > 0
DO
INPUT "vvedite 2 chislo ", b
IF b <= 0 THEN PRINT "nevernyj vvod"
LOOP UNTIL b > 0
X = a
Y = b
DO
IF X > Y THEN X = X - Y ELSE Y = Y - X
LOOP UNTIL X = Y
PRINT "NOD chisel"; a; "i"; b; "="; X
END