给定 $A_1, A_2, \dots, A_n$，请计算满足 $l \le r$ 且 $A_l + A_r = \max_{i=l}^r A_i$ 的合法数对 $(l, r)$ 的数量。
第一行包含一个整数 $n$ ($1 \le n \le 500000$)。
第二行包含 $n$ 个整数，表示 $A_1, A_2, \dots, A_n$ ($0 \le A_i \le 10^9, 1 \le i \le n$)。
输出一个整数，表示合法的 $(l, r)$ 数对的数量。
6 1 3 2 5 7 4
2
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