1 #include<cstdio>
 2 #define F(i,a,b) for(int i=a;i<=b;++i)
 3 
 4 const int N=2e5+7;
 5 int n,m,a[N];
 6     
 7 int main()
 8 {
 9     scanf("%d%d",&n,&m);
10     int now=1;
11     F(i,2,n)
12     {
13         if(i<=m+1)a[i]=1;
14         else a[i]=i-m;
15     }
16     int ans;
17     if((n-1)%m==0)ans=(n-1)/m*2;
18     else if((n-1)%m==1)ans=((n-1)/m*2)+1;
19     else ans=((n-1)/m*2)+2;
20     printf("%d\n",ans);
21     F(i,2,n)printf("%d %d\n",i,a[i]);
22     return 0;
23 }