#include <string>
#include <iostream>
#include <sstream>
#include <vector>
#include <iterator>

template <typename It>
bool seemslegit(It begin, It end) {
    if (std::distance(begin, end) == 1) {
      return true;
    }
    int a = *begin++;
    int b = *begin++;
    if (a == b || std::abs(a-b) > 3) return false;;
    bool increasing = b > a;
    while (begin != end) {
      int c = *begin++;
      if (b == c || std::abs(b-c) > 3) return false;;
      switch (increasing) {
        case false:
          if (c < b) { b = c; continue; }
          return false;
        case true:
          if(c > b) { b = c; continue; }
          return false;
      }
    }
    return true;
}

template <typename It>
void debug(It begin, It end) {
  bool legit = seemslegit(begin, end);
  while (begin != end) {
    std::cout << *begin++ << " ";
  }
  //std::cout << ": " << std::boolalpha << legit << std::endl;
}

int main() {
  int safe = 0;
  std::string s;
  while (std::getline(std::cin, s)) {
    std::istringstream iss(s);
    std::vector<int> report((std::istream_iterator<int>(iss)),
                            std::istream_iterator<int>());
    debug(report.begin(), report.end());
    if (seemslegit(report.begin(), report.end())) {
      safe++;
      std::cout << "\n\n";
      continue;
    }
    for (int i = 0; i < report.size(); ++i) {
      auto report2 = report;
      auto it = report2.erase(report2.begin()+i);
      debug(report2.begin(), report2.end());
      if (seemslegit(report2.begin(), report2.end())) {
        safe++;
        break;
      }
    }
    std::cout << "\n\n";
 }
  std::cout << safe << std::endl;
}

Doing this “efficiently” should be possible. since you only need ~2-ish look-back you should be able to score reports in O(n) time. One complication is you might get the direction wrong, need to consider that erasing one of the first two elements could change the direction. But that requires thinking, and shoving all the permutations into a function with ungodly amounts of copying does not.