package contest200904; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.InputMismatchException; public class C { InputStream is; PrintWriter out; String INPUT = ""; void solve() { int n = ni(); int[] a = na(n); int[] b =new int[n]; for(int i = 0;i < n;i++){ b[i] = i+1 - a[i]; } StarrySkyTreePos sst = new StarrySkyTreePos(b); while(true){ int[] nn = sst.minpos(0, n); int ne = nn[0]; if(ne != 0)break; int cur = nn[1]; sst.add(0, cur, -1); sst.add(cur, cur+1, cur+1); } for(int i = 0;i < n;i++){ if(sst.min(i, i+1) != i+1){ out.println("No"); return; } } out.println("Yes"); } public static class StarrySkyTreePos { public int M, H, N; public int[] st; public int[] plus; public int[] pos; public int I = Integer.MAX_VALUE/4; // I+plus>>1; st = new int[M]; plus = new int[H]; pos = new int[M]; for(int i = M-1;i >= H;i--)pos[i] = i-H; for(int i = H-1;i >= 0;i--)propagate(i); } public StarrySkyTreePos(int[] a) { N = a.length; M = Integer.highestOneBit(Math.max(N-1, 1))<<2; H = M>>>1; st = new int[M]; for(int i = 0;i < N;i++){ st[H+i] = a[i]; } plus = new int[H]; Arrays.fill(st, H+N, M, I); pos = new int[M]; for(int i = M-1;i >= H;i--)pos[i] = i-H; for(int i = H-1;i >= 1;i--)propagate(i); } private void propagate(int i) { if(st[2*i] <= st[2*i+1]){ st[i] = st[2*i] + plus[i]; pos[i] = pos[2*i]; }else{ st[i] = st[2*i+1] + plus[i]; pos[i] = pos[2*i+1]; } } public void add(int l, int r, int v){ if(l < r)add(l, r, v, 0, H, 1); } private void add(int l, int r, int v, int cl, int cr, int cur) { if(l <= cl && cr <= r){ if(cur >= H){ st[cur] += v; }else{ plus[cur] += v; propagate(cur); } }else{ int mid = cl+cr>>>1; if(cl < r && l < mid){ add(l, r, v, cl, mid, 2*cur); } if(mid < r && l < cr){ add(l, r, v, mid, cr, 2*cur+1); } propagate(cur); } } public int min(int l, int r){ return l >= r ? I : min(l, r, 0, H, 1);} private int min(int l, int r, int cl, int cr, int cur) { if(l <= cl && cr <= r){ return st[cur]; }else{ int mid = cl+cr>>>1; int ret = I; if(cl < r && l < mid){ ret = Math.min(ret, min(l, r, cl, mid, 2*cur)); } if(mid < r && l < cr){ ret = Math.min(ret, min(l, r, mid, cr, 2*cur+1)); } return ret + plus[cur]; } } public int[] minpos(int l, int r){ return l >= r ? null : minpos(l, r, 0, H, 1);} private int[] minpos(int l, int r, int cl, int cr, int cur) { if(l <= cl && cr <= r){ return new int[]{st[cur], pos[cur]}; }else{ int mid = cl+cr>>>1; int[] L = null, R = null; if(cl < r && l < mid){ L = minpos(l, r, cl, mid, 2*cur); } if(mid < r && l < cr){ R = minpos(l, r, mid, cr, 2*cur+1); } if(L == null && R == null)return null; if(R == null || L[0] <= R[0]){ L[0] += plus[cur]; return L; }else{ R[0] += plus[cur]; return R; } } } public int[] toArray() { return toArray(1, 0, H, new int[H]); } private int[] toArray(int cur, int l, int r, int[] ret) { if(r-l == 1){ ret[cur-H] = st[cur]; }else{ toArray(2*cur, l, l+r>>>1, ret); toArray(2*cur+1, l+r>>>1, r, ret); for(int i = l;i < r;i++)ret[i] += plus[cur]; } return ret; } } void run() throws Exception { is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); long s = System.currentTimeMillis(); solve(); out.flush(); if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){ // @Override // public void run() { // long s = System.currentTimeMillis(); // solve(); // out.flush(); // if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms"); // } // }; // t.start(); // t.join(); } public static void main(String[] args) throws Exception { new C().run(); } private byte[] inbuf = new byte[1024]; public int lenbuf = 0, ptrbuf = 0; private int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private double nd() { return Double.parseDouble(ns()); } private char nc() { return (char)skip(); } private String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private long[] nal(int n) { long[] a = new long[n]; for(int i = 0;i < n;i++)a[i] = nl(); return a; } private char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private int[][] nmi(int n, int m) { int[][] map = new int[n][]; for(int i = 0;i < n;i++)map[i] = na(m); return map; } private int ni() { return (int)nl(); } private long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { System.out.println(Arrays.deepToString(o)); } }