Help with Runtime Error in my Code

I am getting a runtime error (SIGSEGV) on my code and I don't know how to fix it. Please help. Thanks.

Problem:http://www.codechef.com/problems/POINTS

My Solution:http://www.codechef.com/viewsolution/3127090

My Code:

#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>

using namespace std;
typedef pair<int, int> Coord;
bool second_descend(const pair<int, int>& i, const pair<int, int>& j) {
    if (i.second < j.second) return false;
    if (j.second < i.second) return true;
    return j.first < i.first;
}

float get_distance(Coord a, Coord b){
    return sqrt(pow(b.first - a.first, 2) + pow(b.second - a.second , 2));
}

int main() {

    int t, n;
    Coord coordinate_template;
    cin >> t;

    while (t--){
        vector<Coord> points;
        cin >> n;
        while (n--){
            cin >> coordinate_template.first >> coordinate_template.second;
            points.push_back(coordinate_template);
        }

        sort(points.begin(), points.end());

        for (int a = 0; a < points.size()-2; a++){

            if (points[a].first == points[a + 1].first){

                int counter = a + 1;

                while (points[counter].first == points[a].first){
                    counter++;
                }

                sort(points.begin() + a, points.begin() + counter, second_descend);

            }

        }
        float sum = 0;
        for (int a = 0; a < points.size()-1; a++){
            sum += get_distance(points[a], points[a + 1]);
        }
        cout << floor(sum * 100 + 0.5) / 100 << endl;

    }
    return 0;
}