Problem p01486 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <string>
#include <utility>
#include <vector>

using namespace std;

// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<double> VEC;
typedef vector<VEC> MAT;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef pair<int, TIII> QIIII;
typedef long long LL;
typedef vector<LL> VLL;

// container util

//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())
#define MT(a, b, c) MP(a, MP(b, c))
#define MQ(a, b, c, d) MP(a, MT(b, c, d))
#define Q1 first
#define Q2 second.first
#define Q3 second.second.first
#define Q4 second.second.second

// repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define EPS 1e-8
#define MOD 1000000007

int main() {
  string str;
  cin >> str;
  int n = str.length();
  while (n) {
    string::size_type k = str.find("mew");
    if (k == string::npos) {
      cout << "Rabbit" << endl;
      return 0;
    } else if (k == 0) {
      if (n == 3)
        cout << "Cat" << endl;
      else
        cout << "Rabbit" << endl;
      return 0;
    } else {
      n -= 3;
      str.erase(k, 3);
    }
  }
  return 0;
}

Error: 0

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdio.h>
#include <string>
#include <utility>
#include <vector>

using namespace std;

// conversion
//------------------------------------------
inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}

// typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<double> VEC;
typedef vector<VEC> MAT;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef pair<int, PII> TIII;
typedef pair<int, TIII> QIIII;
typedef long long LL;
typedef vector<LL> VLL;

// container util

//------------------------------------------
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define EXIST(s, e) ((s).find(e) != (s).end())
#define SORT(c) sort((c).begin(), (c).end())
#define MT(a, b, c) MP(a, MP(b, c))
#define MQ(a, b, c, d) MP(a, MT(b, c, d))
#define Q1 first
#define Q2 second.first
#define Q3 second.second.first
#define Q4 second.second.second

// repetition
//------------------------------------------
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(i, n) FOR(i, 0, n)
#define EPS 1e-8
#define MOD 1000000007

int main() {
  string str;
  cin >> str;
  int n = str.length();
  while (n) {
    unsigned int k = str.find("mew");
    if (k == string::npos) {
      cout << "Rabbit" << endl;
      return 0;
    } else if (k == 0) {
      if (n == 3)
        cout << "Cat" << endl;
      else
        cout << "Rabbit" << endl;
      return 0;
    } else {
      n -= 3;
      str.erase(k, 3);
    }
  }
  return 0;
}