func_code_string: #include <bits/stdc++.h>   using namespace std;   bool sortbysec(const pair<int, int> &a, const pair<int, int> &b) {     if (a.second < b.second) return true;     if (a.second == b.second) return a.first < b.first;     return false;   }   bool isprime(int n) {     if (n <= 1) return false;     for (int i = 2; i <= sqrt(n); i++)       if (n % i == 0) return false;     return true;   }   bool isPowerOfTwo(int n) {     if (n == 0) return false;     return (ceil(log2(n)) == floor(log2(n)));   }   int gcd(int a, int b) {     if (a == 0) return b;     return gcd(b % a, a);   }   long long int lcm(long long int a, long long int b) {     return (a / gcd(a, b)) * b;   }   long long int ncr(long long int n, long long int r) {     if (r == 0) return 1;     r = min(r, n - r);     long long int ans = 1;     for (int i = 1; i <= r; i++) {       ans *= (n - i + 1);       ans /= i;     }     return ans;   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     int t = 1;     while (t--) {       int n, m;       cin >> n >> m;       vector<pair<int, int>> v;       int x, y;       for (int i = 0; i < m; i++) {         cin >> x >> y;         v.push_back(make_pair(x, y));       }       int ans = 0;       if (v[0].first != 1) {         cout << 1 <<     << 0 <<   n ;       } else {         int dayno = -1;         for (int i = 1; i < v.size(); i++) {           if (v[i].first == v[i - 1].second) {             ans = 2;             dayno = v[i].first;             int j = i + 1;             while (j < v.size() && v[j].first == v[i].first) ans++, j++;             break;           } else if (v[i].first != v[i - 1].second + 1) {             dayno = v[i - 1].second + 1;             ans = 0;             break;           }         }         if (dayno != -1)           cout << dayno <<     << ans <<   n ;         else {           if (v[v.size() - 1].second != n)             cout << v[v.size() - 1].second + 1 <<     << 0 <<   n ;           else             cout <<  OK                   <<   n ;         }       }     }     return 0;   }   