最简单的区间贪心，但是考察细心。

注意事项：

1、考虑s>t的情况

2、读入的时候要把s、t分别转换为（s+1）div 2和（t+1）div 2

代码：

Program poj1083;//By_ThispoetConst 	maxn=200;Var	t,i,j,k,m,n						:Longint;	heap,l,r						:Array[1..maxn*2]of Longint;	heap_size						:Longint;	Procedure Down(i:Longint);var j:Longint;begin	while ((i<<1)<=heap_size) do 		begin			j:=i<<1;			if (j
     
      heap[j+1])then inc(j);			if heap[j]
      
       1) do 		begin			j:=i>>1;			if heap[j]>heap[i] then 				begin					heap[i]:=heap[i] xor heap[j];					heap[j]:=heap[i] xor heap[j];					heap[i]:=heap[i] xor heap[j];					i:=j;				end else break;		end;end;		Procedure Qsort(ll,rr:Longint);var i,j,k,temp:Longint;begin		i:=ll;j:=rr;	k:=l[i+random(j-i+1)];	repeat		while l[i]
       
        k do dec(j);		if i<=j then 			begin				temp:=l[i];l[i]:=l[j];l[j]:=temp;				temp:=r[i];r[i]:=r[j];r[j]:=temp;				inc(i);dec(j);			end;	until i>j;	if ll
        
         0 do 		begin					heap_size:=0;			readln(n);			for i:=1 to n do 				begin					readln(l[i],r[i]);					if l[i]>r[i] then Swap(l[i],r[i]);					l[i]:=(l[i]+1)>>1;					r[i]:=(r[i]+1)>>1;				end;			Qsort(1,n);			for i:=1 to n do 				begin					if (heap_size>0)and(heap[1]