#/***********************************************************
#    e.rb -- 自然対数の底
#***********************************************************/
def ee
    e = 0;  a = 1.0;  n = 1.0
    begin 
        prev = e;  e += a;  a /= n;  n += 1
    end while (e != prev)
    return e
end

LDBL_DIG = 18
p ee
printf("e = %.*g\n", LDBL_DIG, ee())

exit 0