source_code: import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.util.StringTokenizer;
  
  public class AnnoyingPresent {
  
  	
  	//UPSOLVED
  	public static void main(String[] args) throws IOException {
  
  		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  		StringTokenizer st = new StringTokenizer(br.readLine());
          long n = Long.parseLong(st.nextToken()) , m = Long.parseLong(st.nextToken());
          
          long sum = 0;
          
          for(int i=0;i<m;i++){
          	StringTokenizer st1 = new StringTokenizer(br.readLine());
              sum+= n* Long.parseLong(st1.nextToken());
              Long a= Long.parseLong(st1.nextToken());
              if(a < 0){
                  if(n % 2 == 0)
                      sum += n*n / 4*a;
                  else{
                      sum += (n/2) * (n/2+1) * a;
                  }
              }
              else
                  sum += (a*(n) * (n-1) / 2);
              
          }
          System.out.println((double)sum/n);
  	}
  
  }
  