What's wrong?

#include <iostream>
#include <math.h>
#include <stdio.h>
int _1020()
{
    double r = 0.0; // Радиус шляпок
    int n = 0; // Число гвоздей

    std::cin >> n >> r;
    double f_x = 0.0;
    double f_y = 0.0;
    std::cin >> f_x >> f_y;
    --n;    // Первая строка уже введена

    double length = 0.0;
    double t_x = 0.0;
    double t_y = 0.0;

    double c_x = 0.0;
    double c_y = 0.0;

    for(int i = 0; i < n; i++)
    {
        std::cin >> c_x >> c_y;
        if(i == n-1)
        {
             length += sqrt(pow(f_x - c_x, 2) + pow(f_y - c_y, 2));
        }

        length += sqrt(pow(c_x - t_x, 2) + pow(c_y - t_y, 2));

        t_x = c_x;
        t_y = c_y;
    }
    length += 2*acos(-1.0)*r;

    std::cout.setf(std::ios_base::fixed,std::ios_base::floatfield);
    std::cout.precision(2);
    std::cout << length << "\n";

    return 0;
}

first coordinates differ from 0.0 in that test

Thank u! I got AC

Error was very stupid.. (wrong condition in for(){}) :)