Language: C++

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iomanip>
#include <limits>
#include <bitset>
#include <map>

using namespace std;

typedef long long ll;
typedef pair<int, int> P;
typedef pair<ll, ll> PL;
#define int ll

const ll MOD = 1000000007;
const ll INF_LL = (ll)1000000007 * 1000000007;
const int INF_INT = (int)1000000007;
const double PI = 3.14159265358979323846;

const int dx[4] = { 1, 0, -1, 0 };
const int dy[4] = { 0, 1, 0, -1 };

#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) FOR(i, 0, n)
#define rrep(i, n) for (int i = ((int)(n)-1); i >= 0; i--)
#define irep(itr, st) for (auto itr = (st).begin(); itr != (st).end(); ++itr)
#define irrep(itr, st) for (auto itr = (st).rbegin(); itr != (st).rend(); ++itr)

#define m0(x) memset((x), 0, sizeof((x)))
#define m1(x) memset((x), -1, sizeof((x)))

// xにはvectorなどのコンテナ
#define ALL(x) (x).begin(), (x).end()  // sortなどの引数を省略したい
#define RALL(x) (x).rbegin(), (x).rend()  // sortなどの引数を省略したい
#define SIZE(x) ((ll)(x).size())     // sizeをsize_tからllに直しておく
#define MAX(x) *max_element(ALL(x))  //最大値を求める
#define MIN(x) *min_element(ALL(x))  //最小値を求める
#define all(x) (x).begin(), (x).end()

//略記
#define pb emplace_back  // vectorヘの挿入
#define mp make_pair     // pairのコンストラクタ
#define F first          // pairの一つ目の要素
#define S second         // pairの二つ目の要素

#define BITCOUNT __builtin_popcount
#define BITCOUNT_LL(x) __builtin_popcountll(x)

#define perm(c)             \
  sort(all(c));             \
  for (bool c##p = 1; c##p; \
       c##p = next_permutation(all(c)))  //順列 123 132 213 231 312 321

#define BIT(n) (1LL << (n))

#ifdef DEBUG
#define PRINT(A) std::cout << (#A) << ": " << (A) << std::endl;
#else
#define PRINT(A)
#endif

//入力高速化
struct IoSetup {
    IoSetup() {
        cin.tie(nullptr);
        ios::sync_with_stdio(false);
        cout << fixed << setprecision(20);
    }
} iosetup;

template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}


int bitcount(int bits) {
    int ret = 0;
    while (bits > 0) {
        if (bits & 1) ret++;
        bits = bits >> 1;
    }
    return ret;
}

signed main() {
    string S; cin >> S;
    int K; cin >> K;
    int ans = 0;
    if (K == 1) {
        rep(i, S.length()) {
            if (i == 0)continue;
            if (S[i] == S[i - 1]) {
                S[i] = 1;
                ans += 1;
            }
        }
    }
    else {
        string S2 = S + S;
        string S3 = S + S + S;
        int buf2 = 0;
        int buf3 = 0;
        rep(i, S2.length()) {
            if (i == 0)continue;
            if (S2[i] == S2[i - 1]) {
                S2[i] =  1;
                buf2 += 1;
            }
        }
        rep(i, S3.length()) {
            if (i == 0)continue;
            if (S3[i] == S3[i - 1]) {
                S3[i] =  1;
                buf3 += 1;
            }
        }
        ans = buf2 + (buf3 - buf2) * (K - 2);
    }
    if (S.length() == 1) ans = K / 2;
    int same = 0;
    rep(i, S.length()-1) {
        if (S[i] != S[i + 1) same = 1;
    }
    if (same == 0) ans = S.length() * K / 2;
    cout << ans << endl;
}
 

Compiler output:
a.cc: In function 'int main()':
a.cc:138:28: error: expected ']' before ')' token
  138 |         if (S[i] != S[i + 1) same = 1;
      |                            ^
      |                            ]