1 files changed, 23 insertions, 0 deletions
diff --git a/contests/filtrationContest/C/main.cpp b/contests/filtrationContest/C/main.cpp
new file mode 100644
index 0000000..0d06899
--- /dev/null
+++ b/contests/filtrationContest/C/main.cpp
@@ -0,0 +1,23 @@
+#include<bits/stdc++.h>
+
+using namespace std;
+
+int64_t fq[22];
+
+int main () {
+	ios_base::sync_with_stdio(false);
+	cin.tie(NULL);
+  long long n;
+  cin >> n;
+  for (int i = 1; i <= n; i++) {
+    int64_t x;
+    cin >> x;
+    fq[10 + x]++;
+  }
+  int64_t ans = 0;
+  for (int i = 1;i <= 10; i++) {
+    ans += fq[10 - i] * fq[10 + i];
+  }
+  ans += fq[10] * (fq[10] - 1) / 2;
+  cout << ans;
+}