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#include <bits/stdc++.h>
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using namespace std;
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const int N = 110;
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/*
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由于每个数的范围都在10000以内，因此两个数的和在20000以内，所以可以开一个长度是20000的bool数组，
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然后枚举所有数对，将所有计算出的两数之和标记一下。
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然后再枚举每个数，利用bool数组判断它是否是某两个数的和。
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*/
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int n;
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int a[N];
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bool st[20010];
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int main() {
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scanf("%d", &n);
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for (int i = 0; i < n; i++) scanf("%d", &a[i]);
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for (int i = 0; i < n; i++)
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for (int j = 0; j < i; j++)
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st[a[i] + a[j]] = 1;
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int res = 0;
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for (int i = 0; i < n; i++) res += st[a[i]];
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printf("%d\n", res);
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return 0;
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}
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