x = "/home/user1/tmp/coverage/test"
y = "/home/user1/tmp/covert/operator"
z = "/home/user1/tmp/coven/members"

a = length(x)
if a > length(y) then a = length(y)
if a > length(z) then a = length(z)
for i = 1 to a
    if mid(x, i, 1) <> mid(y, i, 1) then exit for
next i
a = i - 1

for i = 1 to a
    if mid(x, i, 1) <> mid(z, i, 1) then exit for
next i
a = i - 1

if mid(x, i, 1) <> "/" then
    for i = a to 1 step -1
        if "/" = mid(x, i, 1) then exit for
    next i
end if

REM Task description says no trailing slash, so...
a = i - 1
print "Common path is '"; left(x, a); "'"