A format for expressing an ordered list of integers is to use a comma separated list of either
* individual integers
* or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. The range includes all integers in the interval including both endpoints.  It is not considered a range unless it spans at least 3 numbers. For example "12,13,15-17"
Complete the solution  so that it takes a list of integers in increasing order and returns a correctly formatted string in the range format. 
**Example:**
```python
solution([-6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20])
# returns "-6,-3-1,3-5,7-11,14,15,17-20"
```
```C#
RangeExtraction.Extract(new[] {-6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20});
# returns "-6,-3-1,3-5,7-11,14,15,17-20"
```
*Courtesy of rosettacode.org*
def solution(args):
    result = ""
    i = 0
    while i<len(args):
        val = args[i]
        while i+1<len(args) and args[i]+1==args[i+1]:
            i+=1
        if val == args[i]:
            result += ",%s"%val
        elif val+1 == args[i]:
            result += ",%s,%s"%(val, args[i])
        else:
            result += ",%s-%s"%(val, args[i])
        i+=1
    return result.lstrip(",")
def solution(args):
    result = ""
    i = 0
    while i<len(args):
        val = args[i]
        while i+1<len(args) and args[i]+1==args[i+1]:
            i+=1
        if val == args[i]:
            result += ",%s"%val
        elif val+1 == args[i]:
            result += ",%s,%s"%(val, args[i])
        else:
            result += ",%s-%s"%(val, args[i])
        i+=1
    return result.lstrip(",")