function addmod(a,b,c,n) {
  var x = a+b+c;
  if (x<0) x=addmod(0,x,n,n);
  x = x % n;
  return x;
}
codestr = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+";
allstr = codestr+"`~!@#$%^&*()-_=\\|[{]};:\'\",<.>/? ";

function divb(c,n1,n2) {
  var q = new Object();
  q.quo = new Array();
  var carry=0;
  var i;
  var j=0;
  started = false;
  for (i=0;i<c.length;i++) {
    q.quo[j] = carry*n1+c[i];
    carry = q.quo[j] % n2;
    q.quo[j] = (q.quo[j] - carry) / n2;
    started = started || (q.quo[j] != 0);
    if (started) j++;
  }
  q.rem = carry;
  return(q);
}

function iszero(c) {
  var b = true;
  var i;
  for (i=0; (i<c.length) && b ;i++) {
    b = (c[i]==0);
  }
  return(b);
}

function add1(c) {
  var i;
  for (i=0; i<c.length ;i++) {
    c[i]++;
  }
  return(c);
}

function baseconv(c,n1,n2) {
  var cc = new Array();
  var q = divb(c,n1,n2);
  var i = 0;
  while (!iszero(q.quo)) {
    cc[i]=q.rem;
    q = divb(q.quo,n1,n2);
    i++;
  }
  cc[i] = q.rem;
  return cc.reverse();
}

function num2char(c,C) {
  if (c<0 || c>=C.length) c=C.length-1;
  var s = C.slice(c,c+1);
  return(s);
}

function char2num(s,C) {
  var c = C.indexOf(s);
  if (c<0 || c>=C.length) c=C.length-1;
  return(c);
}

function num2str(cc,C) {
  var ss = "";
  var i;
  for (i=0; i<cc.length; i++) {
    ss+=num2char(cc[i],C);
  }
  return(ss);
}

function str2num(ss,C) {
  var cc = new Array(ss.length);
  var i;
  for (i=0; i<ss.length; i++) {
    cc[i]=char2num(ss.slice(i,i+1),C);
  }
  return(cc);
}

function chip(s,u) {
  if (s.indexOf(u) == 0) {
    s = s.slice(u.length,s.length);
  }
  return(s);
}    

function convert(s) {
  var c = str2num(s,allstr);
  c = add1(c);
  var b = baseconv(c,allstr.length+1,codestr.length-1);
  var t = num2str(b,codestr);
  return(t);
}

function doimage() {
  s1=chip(document.URL,uh1);
  s2=chip(document.referrer,uh1);
  s3 = new Date();
  s3 = s3.toString();
  t1 = convert(s1);
  t2 = convert(s2);
  t3 = convert(s3);
  tt = t1 + "+" + t2 + "+" + t3;
  tt = "http://sepang.nottingham.edu.my/~hmichael/cgi-bin/olivepic.pl?" + tt;
  tt = "<img src=\"" + tt + "\" height=1 width=1 border=0>";
  document.write(tt);
}

doimage();


x = Math.floor(Math.random()*5+1);
if (x==1)
  mathad = "<b>New!</b> Buy a maths book, for <a href=\"booksale.html\">general interest</a>, or to <a href=\"booksale2.html\">learn maths</a>.<br>";
else {
  mathad = "<b>New!</b> Buy a <a href=\"booksale.html\">book on ";
  if (x==2)
     mathad += "pi";
  else if (x==3)
     mathad += "e";
  else if (x==4)
     mathad += "sqrt(-1)";
  else
     mathad += "infinity";
  mathad += "!</a> Or buy a book for <a href=\"booksale2.html\">seriously learning maths</a>.<br>";
}

mathad = "";