#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;

bool is_valid_filename(const char* filename) {
    const char* invalid_chars = "*<>?|";
    if (strpbrk(filename, invalid_chars)) return false;

    const char* colon = strchr(filename, ':');
    if (colon && (colon != filename + 1 || !isalpha(filename[0]) || colon[1] != '\n')) return false;

    const char* ext = strrchr(filename, '.');
    if (ext && strcasecmp(ext, ".txt") != 0) return false;

    return true;
}

void add_txt_extension(char* filename) {
    strcat(filename, ".txt");
}

int main() {
    char filename[256];
    cout << "Enter filename: ";
    cin >> filename;

    if (!is_valid_filename(filename)) {
        cout << "Invalid filename." << endl;
        return 1;
    }

    if (!strrchr(filename, '.')) add_txt_extension(filename);

    ifstream file(filename, ios::binary | ios::ate);
    if (!file.is_open()) {
        cout << "Failed to open file." << endl;
        return 1;
    }

    streamsize size = file.tellg();
    file.seekg(0, ios::beg);

    char* buffer = new char[size];
    file.read(buffer, size);

    char search[256];
    cout << "Enter string to search: ";
    cin >> search;

    size_t count = 0;
    char* pos = buffer;
    while ((pos = strstr(pos, search))) {
        ++count;
        pos += strlen(search);
    }

    cout << "Occurrences: " << count << endl;

    delete[] buffer;
    return 0;
}