#include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; } template inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); } template inline T sqr(T x) { return x*x; } typedef vector VI; typedef vector VVI; typedef vector VS; typedef pair PII; typedef long long ll; //repetition //------------------------------------------ #define FOR(i,a,b) for(int i=(a);i<(b);++i) #define rep(i,n) FOR(i,0,n) #define P(p) cout<<(p)< >(a, vector(b, 0)) #define ALL(a) (a).begin(),(a).end() #define RALL(a) (a).rbegin(), (a).rend() #define pb push_back #define mp make_pair #define INF (1100000000) #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 MOD 1000000007LL int gcd(int x, int y) { if (y == 0) return x; else return gcd(y, x%y); } int lcm(int a, int b) { return a / gcd(a, b) * b; } bool is_prime(int n) { for (int i = 2; i * i <= n; i++) { if (n % i == 0) return false; } return n != 1; } map prime_factor(int n) { map res; for (int i = 2; i * i <= n; i++) { while (n % i == 0) { ++res[i]; n /= i; } } if (n != 1) res[n] = 1; return res; } int extgcd(int a, int b, int& x, int& y) {// int d = a; if (b != 0) { d = extgcd(b, a%b, y, x); y -= (a / b)*x; } else { x = 1; y = 0; } return d; } ll mod_pow(ll x, ll n, ll mod) { if (n == 0) return 1; ll res = mod_pow(x * x % mod, n / 2, mod); if (n & 1) res = res * x % mod; return res; } vector split(const string &str, char delim) { vector res; size_t current = 0, found; while ((found = str.find_first_of(delim, current)) != string::npos) { res.push_back(string(str, current, found - current)); current = found + 1; } res.push_back(string(str, current, str.size() - current)); return res; } bool is_kadomatsu(int a, int b, int c) { if (a == b || a == c || b == c)return false; if (a > b && c > b) return true; if (a < b && c < b)return true; return false; } struct edge { int from, to, cost; edge(){} edge(int f, int t, int c) { from = f; to = t; cost = c; } }; bool cmp(const edge & e1, const edge& e2) { return e1.cost < e2.cost; } int main() { int N,K; cin >> N >>K; VI a1, a2; rep(i, N) { int a; cin >> a; a1.push_back(a); } int ans = 0; rep(i, N) { for (int j = 0; j + K < N; j++) { if (a1[j] > a1[j + K]) { swap(a1[j], a1[j + K]); ans++; } } } rep(i, N - 1) { if (a1[i] > a1[i + 1]) { P(-1); return 0; } } P(ans); return 0; }