PROGRAMMING:Iceman rescue operation
Little Iceman and little fireman are best friends. Little Iceman is trapped. Little fireman is going to rescue him now. The location of the little fireman is s, and the location of the Iceman is D. We only know the distance between every two neighboring cities (not unique). Now we need to find the shortest path from s to D, and let the little fireman rescue the little Iceman.
###Input format:
Input Description: the first line of the input data gives four positive integers n, m, s, D, where n is the number of cities, assuming that the number of cities is 0 ~ (n − 1); M is the number of highways; S is the position of little fireman; D is the location of the little Iceman. In the following M line, each line gives the information of a road, which are: City 1, city 2 and road length, separated by spaces, and the numbers are all integers. Input guarantees the existence of solutions.
###Output format:
The size of the shortest path.
###Input example:
Here is a set of inputs. For example:
```in
4 5 0 3
0 1 1
1 3 2
0 3 4
0 2 2
2 3 1
```
###Output example:
The corresponding output is given here. For example:
```out
three
```
answer：If there is no answer, please comment
###Input format:
Input Description: the first line of the input data gives four positive integers n, m, s, D, where n is the number of cities, assuming that the number of cities is 0 ~ (n − 1); M is the number of highways; S is the position of little fireman; D is the location of the little Iceman. In the following M line, each line gives the information of a road, which are: City 1, city 2 and road length, separated by spaces, and the numbers are all integers. Input guarantees the existence of solutions.
###Output format:
The size of the shortest path.
###Input example:
Here is a set of inputs. For example:
```in
4 5 0 3
0 1 1
1 3 2
0 3 4
0 2 2
2 3 1
```
###Output example:
The corresponding output is given here. For example:
```out
three
```
answer：If there is no answer, please comment