Problem p03569 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
using namespace std;
//---------------------------------------------------
// ライブラリゾーン！！！！
#define int long long
#define str string
#define rep(i, j) for (int i = 0; i < (int)(j); i++)
typedef long long ll;
typedef long double ld;
const ll inf = 4523372036854775807;
short gh[2][4] = {{0, 0, -1, 1}, {-1, 1, 0, 0}};
struct P {
  ll pos, cost;
};
bool operator<(P a, P b) { return a.cost < b.cost; }
bool operator>(P a, P b) { return a.cost > b.cost; }
struct B { // 隣接リスト表現
  ll to, cost;
};
struct S { // 辺の情報を入れる変数
  int from, to, cost;
};
struct H {
  int x, y;
};
bool operator<(H a, H b) {
  if (a.x != b.x)
    return a.x < b.x;
  return a.y < b.y;
}
bool operator>(H a, H b) {
  if (a.x != b.x)
    return a.x > b.x;
  return a.y > b.y;
}
ll gcm(ll i, ll j) { // 最大公約数
  if (i > j)
    swap(i, j);
  if (i == 0)
    return j;
  return gcm(j % i, i);
}
ld rad(ld a, ld b, ld c, ld d) {
  return sqrt(pow(a - c, 2) + pow(b - d, 2));
} // rad＝座標上の2点間の距離
int ari(int a, int b, int c) { return (a + b) * c / 2; } // 等差数列の和
bool suf(ld a, ld b, ld c, ld d) {
  if (b <= c || d <= a)
    return 0;
  return 1;
} //[a,b),[c,d)
//---------------------------------------------------
//+++++++++++++++++++++++++++++++++++++++++++++++++++
signed main() {
  string s, a = "";
  cin >> s;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] != 'x')
      a += s[i];
  }
  bool l = 1;
  for (int i = 0; i < ceil(a.size() / 2.0); i++) {
    if (a[i] != a[a.size() - i - 1])
      l = 0;
  }
  if (!l) {
    cout << -1 << endl;
    return 0;
  }
  int e = s.size() - 1, sum = 0, i = 0;
  while (i != e) {
    if (s[i] != s[e]) {
      sum++;
      if (s[e] == 'x')
        e--;
      else
        i++;
    } else
      e--, i++;
  }
  cout << sum << endl;
  getchar();
  getchar();
}

Fixed submission:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <string>
#include <unordered_map>
#include <vector>
using namespace std;
//---------------------------------------------------
// ライブラリゾーン！！！！
#define int long long
#define str string
#define rep(i, j) for (int i = 0; i < (int)(j); i++)
typedef long long ll;
typedef long double ld;
const ll inf = 4523372036854775807;
short gh[2][4] = {{0, 0, -1, 1}, {-1, 1, 0, 0}};
struct P {
  ll pos, cost;
};
bool operator<(P a, P b) { return a.cost < b.cost; }
bool operator>(P a, P b) { return a.cost > b.cost; }
struct B { // 隣接リスト表現
  ll to, cost;
};
struct S { // 辺の情報を入れる変数
  int from, to, cost;
};
struct H {
  int x, y;
};
bool operator<(H a, H b) {
  if (a.x != b.x)
    return a.x < b.x;
  return a.y < b.y;
}
bool operator>(H a, H b) {
  if (a.x != b.x)
    return a.x > b.x;
  return a.y > b.y;
}
ll gcm(ll i, ll j) { // 最大公約数
  if (i > j)
    swap(i, j);
  if (i == 0)
    return j;
  return gcm(j % i, i);
}
ld rad(ld a, ld b, ld c, ld d) {
  return sqrt(pow(a - c, 2) + pow(b - d, 2));
} // rad＝座標上の2点間の距離
int ari(int a, int b, int c) { return (a + b) * c / 2; } // 等差数列の和
bool suf(ld a, ld b, ld c, ld d) {
  if (b <= c || d <= a)
    return 0;
  return 1;
} //[a,b),[c,d)
//---------------------------------------------------
//+++++++++++++++++++++++++++++++++++++++++++++++++++
signed main() {
  string s, a = "";
  cin >> s;
  for (int i = 0; i < s.size(); i++) {
    if (s[i] != 'x')
      a += s[i];
  }
  bool l = 1;
  for (int i = 0; i < ceil(a.size() / 2.0); i++) {
    if (a[i] != a[a.size() - i - 1])
      l = 0;
  }
  if (!l) {
    cout << -1 << endl;
    return 0;
  }
  int e = s.size() - 1, sum = 0, i = 0;
  while (i < e) {
    if (s[i] != s[e]) {
      sum++;
      if (s[e] == 'x')
        e--;
      else
        i++;
    } else
      e--, i++;
  }
  cout << sum << endl;
  getchar();
  getchar();
}