import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.Comparator; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.TreeSet; public class Main { public static int w; public static int k; // public static int n; // public static int[][] dp; // public static int[] r; // public static long[] buy; // public static List list = new ArrayList(); // public static TreeSet set = new TreeSet(); // public static PriorityQueue pq = new PriorityQueue(); public static void main(String[] args) throws NumberFormatException, IOException{ ContestScanner in = new ContestScanner(); int n = in.nextInt(); int count = 0; int[] renga = new int[n]; int rengaNum = 0; for(int i=0; i= rengaNum){ base = i; break; } } base = base*2-1; int max = Math.min(base, n); int subc = 0; for(int i=0; i 0) count += val; }else{ int val = renga[i] - (n-i); if(val > 0) count += val; } } if(base < n){ for(int i=base; i n){ int[] renga2 = new int[base]; for(int i=0; i 0) subc += val; }else{ int val = renga2[i] - (n-i); if(val > 0) subc += val; } } } count = Math.max(count, subc); System.out.println(count); } } class Range> implements Comparable>{ T start; T end; public Range(T start, T end){ this.start = start; this.end = end; } public boolean inRange(T val){ if(start.compareTo(val) <= 0 && end.compareTo(val) >= 0){ return true; } return false; } public boolean isCommon(Range range){ if(inRange(range.start) || inRange(range.end) || range.inRange(start)){ return true; } return false; } public Range connect(Range range){ if(!isCommon(range)) return null; Range res = new Range(start.compareTo(range.start) <= 0 ? start : range.start, end.compareTo(range.end) >= 0 ? end : range.end); return res; } public boolean connectToThis(Range range){ if(!isCommon(range)) return false; start = start.compareTo(range.start) <= 0 ? start : range.start; end = end.compareTo(range.end) >= 0 ? end : range.end; return true; } @Override public int compareTo(Range range) { int res = start.compareTo(range.start); if(res == 0) return end.compareTo(range.end); return res; } public String toString(){ return "["+start+","+end+"]"; } } class RangeSet>{ TreeSet> ranges = new TreeSet>(); public void add(Range range){ Range con = ranges.floor(range); if(con != null){ if(con.connectToThis(range)) range = con; } con = ranges.ceiling(range); while(con != null && range.connectToThis(con)){ ranges.remove(con); con = ranges.ceiling(range); } ranges.add(range); } public String toString(){ StringBuilder bld = new StringBuilder(); for(Range r: ranges){ bld.append(r+"\n"); } return bld.toString(); } } class Node{ int id; List edge = new ArrayList(); public Node(int id){ this.id = id; } public void createEdge(Node node){ edge.add(node); } } class MyMath{ public static long fact(long n){ long res = 1; while(n > 0){ res *= n--; } return res; } public static long[][] pascalT(int n){ long[][] tri = new long[n][]; for(int i=0; i{ public int compare(Integer arg0, Integer arg1) { return arg0 - arg1; } } class ContestScanner{ private BufferedReader reader; private String[] line; private int idx; public ContestScanner() throws FileNotFoundException{ reader = new BufferedReader(new InputStreamReader(System.in)); } public String nextToken() throws IOException{ if(line == null || line.length <= idx){ line = reader.readLine().trim().split(" "); idx = 0; } return line[idx++]; } public long nextLong() throws IOException, NumberFormatException{ return Long.parseLong(nextToken()); } public int nextInt() throws NumberFormatException, IOException{ return (int)nextLong(); } public double nextDouble() throws NumberFormatException, IOException{ return Double.parseDouble(nextToken()); } }