package no366; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.ArrayList; import java.util.InputMismatchException; import java.util.NoSuchElementException; public class Main { public static void main(String[] args) { IO io = new IO(); int n = io.nextInt(); int k = io.nextInt(); int[] a = io.nextIntArray(n); long cost = 0; for(int i=0;i al = new ArrayList<>(); for(int j=i;j= a[i+1]) { System.out.println("-1"); return; } } System.out.println(cost); } //naive public static long inversionNumber(ArrayList al) { long count = 0; int n = al.size(); for(int i=0;i al.get(j)) { count++; } } } return count; } } class IO extends PrintWriter { private final InputStream in; private final byte[] buffer = new byte[1024]; private int ptr = 0; private int buflen = 0; public IO() { this(System.in);} public IO(InputStream source) { super(System.out); this.in = source;} private boolean hasNextByte() { if (ptr < buflen) { return true; }else{ ptr = 0; try { buflen = in.read(buffer); } catch (IOException e) { e.printStackTrace(); } if (buflen <= 0) { return false; } } return true; } private int readByte() { if (hasNextByte()) return buffer[ptr++]; else return -1;} private static boolean isPrintableChar(int c) { return 33 <= c && c <= 126;} private static boolean isNewLine(int c) { return c == '\n' || c == '\r';} public boolean hasNext() { while(hasNextByte() && !isPrintableChar(buffer[ptr])) ptr++; return hasNextByte();} public boolean hasNextLine() { while(hasNextByte() && isNewLine(buffer[ptr])) ptr++; return hasNextByte();} public String next() { if (!hasNext()) { throw new NoSuchElementException(); } StringBuilder sb = new StringBuilder(); int b = readByte(); while(isPrintableChar(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public char[] nextCharArray(int len) { if (!hasNext()) { throw new NoSuchElementException(); } char[] s = new char[len]; int i = 0; int b = readByte(); while(isPrintableChar(b)) { if (i == len) { throw new InputMismatchException(); } s[i++] = (char) b; b = readByte(); } return s; } public String nextLine() { if (!hasNextLine()) { throw new NoSuchElementException(); } StringBuilder sb = new StringBuilder(); int b = readByte(); while(!isNewLine(b)) { sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } public long nextLong() { if (!hasNext()) { throw new NoSuchElementException(); } long n = 0; boolean minus = false; int b = readByte(); if (b == '-') { minus = true; b = readByte(); } if (b < '0' || '9' < b) { throw new NumberFormatException(); } while(true){ if ('0' <= b && b <= '9') { n *= 10; n += b - '0'; }else if(b == -1 || !isPrintableChar(b)){ return minus ? -n : n; }else{ throw new NumberFormatException(); } b = readByte(); } } public int nextInt() { long nl = nextLong(); if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) { throw new NumberFormatException(); } return (int) nl; } public char nextChar() { if (!hasNext()) { throw new NoSuchElementException(); } return (char) readByte(); } public double nextDouble() { return Double.parseDouble(next());} public int[] nextIntArray(int n) { int[] a = new int[n]; for(int i=0;i