#include using namespace std; int main(){ int n, k; cin >> n >> k; vector A(n); copy_n(istream_iterator(cin), n, A.begin()); k--; if (A[k] == 0){ puts("0"); return 0; } int64_t f = 0; for (int i = k - 1; i >= 0; i--){ f += A[i]; if (A[i] < 2) break; } int64_t b = 0; for (int i = k + 1; i < n; i++){ b += A[i]; if (A[i] < 2) break; } if (A[k] == 1){ cout << max(f, b) + A[k] << endl; } else { cout << f + b + A[k] << endl; } }