Problem p02697 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <bitset>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop                                                                   \\
  char nyaa;                                                                   \\
  cin >> nyaa;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define Per(i, sta, n) for (int i = n - 1; i >= sta; i--)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef long double ld;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};

int n, m;
vector<P> ans;

void solve() {
  cin >> n >> m;
  // int l=(m+1)/2;
  for (int i = m; i >= 1; i -= 1) {
    if (m - i >= i)
      break;
    ans.emplace_back(m - i, i);
  }
  for (int i = m - 1; i >= 1; i -= 1) {
    if (2 * m - i >= m + 1 + i)
      break;
    ans.emplace_back(2 * m - i, m + 1 + i);
  }
  rep(i, m) { cout << ans[i].first + 1 << " " << ans[i].second + 1 << endl; }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(50);
  solve();
}

Error: WA

Fixed submission:

#include <algorithm>
#include <bitset>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
const ll INF = (ll)1000000007 * 1000000007;
typedef pair<int, int> P;
#define stop                                                                   \\
  char nyaa;                                                                   \\
  cin >> nyaa;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define Per(i, sta, n) for (int i = n - 1; i >= sta; i--)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef long double ld;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ll, ll> LP;
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};

int n, m;
vector<P> ans;

void solve() {
  cin >> n >> m;
  // int l=(m+1)/2;
  for (int i = m; i >= 1; i -= 1) {
    if (m - i >= i)
      break;
    ans.emplace_back(m - i, i);
  }
  for (int i = m - 1; i >= 1; i -= 1) {
    ans.emplace_back(2 * m - i, m + 1 + i);
    if (2 * m - 1 >= m + 1 + i)
      break;
  }
  rep(i, m) { cout << ans[i].first + 1 << " " << ans[i].second + 1 << endl; }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(50);
  solve();
}