import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	}

} import java.util.Arrays; Arrays java.util import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	} main {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int cnt = sc.nextInt(); cnt sc.nextInt() sc.nextInt sc double[] nums = new double[cnt]; nums new double[cnt] cnt for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		} int i = 0; int i = 0; i 0 i < cnt i cnt i++ i++ i {
			nums[i] = sc.nextInt();
		} {
			nums[i] = sc.nextInt();
		} nums[i] = sc.nextInt() nums[i] nums i sc.nextInt() sc.nextInt sc Arrays.sort(nums) Arrays.sort Arrays nums int process = 0; process 0 double convert = -1; convert -1 1 while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		} true {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		} double a = 0; a 0 double b = 0; b 0 if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			} convert != -1 convert -1 1 {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				} process == cnt - 1 process cnt - 1 cnt 1 {
					a = nums[process];
					b = convert;
					process = process + 1;
				} a = nums[process] a nums[process] nums process b = convert b convert process = process + 1 process process + 1 process 1 {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				} if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					} nums[process + 1] > convert nums[process + 1] nums process + 1 process 1 convert {
						a = nums[process];
						b = convert;
						process = process + 1;
					} a = nums[process] a nums[process] nums process b = convert b convert process = process + 1 process process + 1 process 1 {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					} a = nums[process] a nums[process] nums process b = nums[process + 1] b nums[process + 1] nums process + 1 process 1 process = process + 2 process process + 2 process 2 {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			} a = nums[process] a nums[process] nums process b = nums[process + 1] b nums[process + 1] nums process + 1 process 1 process = process + 2 process process + 2 process 2 convert = (a + b) / 2 convert (a + b) / 2 (a + b) a b 2 if (process == cnt) {
				break;
			} process == cnt process cnt {
				break;
			} break; System.out.println(convert) System.out.println System.out System System.out convert String[] args args public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	}

} Main
import java.util.Arrays;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);

		int cnt = sc.nextInt();
		double[] nums = new double[cnt];
		for (int i = 0; i < cnt; i++) {
			nums[i] = sc.nextInt();
		}

		Arrays.sort(nums);

		int process = 0;
		double convert = -1;

		while (true) {
			double a = 0;
			double b = 0;
			if (convert != -1) {
				if (process == cnt - 1) {
					a = nums[process];
					b = convert;
					process = process + 1;
				} else {
					if (nums[process + 1] > convert) {
						a = nums[process];
						b = convert;
						process = process + 1;
					} else {
						a = nums[process];
						b = nums[process + 1];
						process = process + 2;
					}
				}
			} else {
				a = nums[process];
				b = nums[process + 1];
				process = process + 2;
			}
			convert = (a + b) / 2;
			if (process == cnt) {
				break;
			}
		}
		System.out.println(convert);
	}

}
