Main

TaskC.java

package com.mehdi.main.codeforces.edu_47;

import com.mehdi.lib.io.InputReader;
import java.io.PrintWriter;

import static com.mehdi.lib.Factories.*;

public class TaskC {

  public void solve(int testNumber, InputReader in, PrintWriter out) {
    int n = in.nextInt();
    int q = in.nextInt();
    double all = 0;
    for (int i = 0; i < q; i++) {
      double x = in.nextInt();
      double d = in.nextInt();
      double max = x * n + d * ((n - 1) * (double)(n) / 2.0);
      double min = 0;
      double size = n / 2;
      min = x + 2.0 * (x * size + d * extractSum(size));
      if (n % 2 == 0) {
        min -= d * size;
      }
      all += Math.max(min, max);
    }
    out.printf("%.8f", all / (double) n);
  }


  private double extractSum(double n) {
    if(n == 1.0) return 1;
    return (n - 1) * (n) / 2.0;
  }
}