#include #define REP(i, n) for(int i = 0; i < n; i++) #define REPR(i, n) for(int i = n; i >= 0; i--) #define FOR(i, m, n) for(int i = m; i < n; i++) #define INF 2e9 #define ALL(v) (v).begin(), (v).end() using namespace std; typedef long long ll; int GCD(int a,int b){return b?GCD(b,a%b):a;} int LCM(int a,int b){return (a*b)/GCD(a,b);} int abs(int x){return x>0?x:-x;} //const int dx[] = {1, 0, -1, 0, 1, -1, -1, 1}; //const int dy[] = {0, 1, 0, -1, 1, 1, -1, -1}; int main() { int l, k; cin >> l >> k; int ans = 0; while (1){ if (l - 2*k <= 0){ cout << ans << endl; return 0; } else { ans += k; l -= 2*k; } } }