20241030 md's submission for cf621c (#8022)

daily_problems/2024/10/1030/personal_submission/cf621c_md.cpp

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+// 1030
+#include <bits/stdc++.h>
+using i64 = long long;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    int n, p;
+    std::cin >> n >> p;
+    std::vector<double> probs(n);
+    for (int i = 0; i < n; ++i) {
+        int left, right;
+        std::cin >> left >> right;
+        probs[i] = 1.0 * (right / p - (left - 1) / p) / (right - left + 1);
+    }
+
+    double ret = 0;
+    for (int i = 0; i < n; ++i) {
+        auto next = (i + 1) % n;
+        ret += probs[i] + probs[next] - probs[i] * probs[next];
+    }
+
+    std::cout << std::fixed << std::setprecision(10) << ret * 2000 << '\n';
+
+    return 0;
+}