src.c:1:3: error: expected expression before 'float'
a=float(input(''))
^
src.c:1:15: error: empty character constant
a=float(input(''))
^
src.c:2:15: error: empty character constant
b=float(input(''))
^
src.c:3:1: error: missing terminating ' character
print(format(a*b/2,'.2f))
^