{"trustable":false,"sections":[{"title":"描述","value":{"format":"MD","content":"数轴上有 n (1\u003c\u003dn\u003c\u003d25000)个闭区间 [ai, bi],选择尽量少的区间覆盖一条指定线段 [1, t]( 1\u003c\u003dt\u003c\u003d1,000,000)。\n覆盖整点,即(1,2)+(3,4)可以覆盖(1,4)。\n不可能办到输出-1"}},{"title":"输入","value":{"format":"MD","content":"\n 第一行:N和T\n 第二行至N+1行: 每一行一个闭区间。"}},{"title":"输出","value":{"format":"MD","content":"选择的区间的数目,不可能办到输出-1"}},{"title":"样例输入","value":{"format":"MD","content":"3 10\n1 7\n3 6\n6 10"}},{"title":"样例输出","value":{"format":"MD","content":"2"}},{"title":"提示","value":{"format":"MD","content":"\n 这道题输入数据很多,请用scanf而不是cin\n "}}]}