diff --git a/3sem/data structures and algos/01/protecc.cpp b/3sem/data structures and algos/01/protecc.cpp
new file mode 100644
index 0000000..adc1d34
--- /dev/null
+++ b/3sem/data structures and algos/01/protecc.cpp	
@@ -0,0 +1,74 @@
+// dsaa_01_prot.cpp
+// Горбацевич Андрей
+#include <iostream>
+#include <map>
+
+#ifdef DEBUG
+#define printf_d printf
+#else
+#define printf_d(...);
+#endif
+
+class FS {
+public:
+    typedef double long_type;
+
+    long_type sum_factor(int N) {
+        long_type sum = 1;
+        this->find_val(N, sum);
+        return sum;
+    }
+
+private:
+    std::map<int, long_type> cache_vals = { {0, 0} };
+    void find_val(int N, long_type &out) {  // O(log(cache_vals.size()))^2)
+        auto it = this->cache_vals.find(N);  // O(log(cache_vals.size())))
+        if (it == this->cache_vals.end()) {
+            printf_d("[Need to calculate sum(1..%d)!]\n", N);
+            long_type _out, _fac;
+            this->find_val(N-1, _out);
+            this->find_factorial(N, _fac);
+            out = _out + _fac;
+            cache_vals[N] = out;  // O(log(cache_vals.size())))
+        }
+        else {
+            out = it->second;
+        }
+    }
+
+    std::map<int, long_type> cache_factorials = { {0, 1} };
+    void find_factorial(int N, long_type &out) {  // O(log(cache_factorials.size()))^2)
+        auto it = this->cache_factorials.find(N);  // O(log(cache_factorials.size())))
+        if (it == this->cache_factorials.end()) {
+            printf_d("[Need to calculate %d!]\n", N);
+            long_type _out;
+            this->find_factorial(N-1, _out);
+            out = _out * N;
+            cache_factorials[N] = out;  // O(log(cache_factorials.size())))
+        }
+        else {
+            out = it->second;
+        }
+    }
+};
+
+int main() {
+    FS _fs;
+
+    do {
+        int i;
+        std::cout << "N=";
+        std::cin >> i;
+
+        if (i == 0) {
+            std::cout << "Goodbye" << std::endl;
+            break;
+        }
+
+        std::cout << "sum (i=1..N) N! = " << _fs.sum_factor(i) << std::endl;
+    } while (true);
+
+    return 0;
+}
+
+