int[] new_stack() {
  var s = new int[7];
  s[0] = 5;
  s[1] = 0; /* current index of stack ptr (offset 2) */
  return s;
}

int peek_stack(int[] s) {
  var index = 1 + s[1];
  return s[index];
}

int[] pop_stack(int[] s) {
  var cur_index = s[1];
  if(cur_index > 0) {
    cur_index = cur_index - 1;
  }

  s[1] = cur_index;
  return maybe_new_stack(s);
}

int[] push_stack(int[] s, int v) {
  var cur_index = 2 + s[1];
  s[cur_index] = v;
  s[1] = cur_index - 1;
  
  return maybe_new_stack(s);
}

int[] maybe_new_stack(int[] s) {
  /* if index of s > half the size, double the size of s */
  /* if index of s < quarter the size, half the size of s */

  return s;

  var cur_index = s[1];
  var cur_size = s[0];

  if(cur_size <= 5) {
    /* min size is 5 */
    return s;
  }

  if(cur_index > (cur_size << 1)) {
    /* double size of s */
    var new_s = new int[2 + cur_size * 2];
    cur_size = cur_size * 2;
    new_s[0] = cur_size;
    new_s[1] = cur_index;

    /* copy over values */
    for(var i = 0; i <= cur_index; i = i + 1;) {
      new_s[2 + i] = s[2 + i];
    }

    return new_s;
  } else if(cur_index < ((cur_size << 1) << 1)) {
    /* halve s */
    var new_s = new int[2 + cur_size << 1];
    cur_size = cur_size << 1;
    new_s[0] = cur_size;
    new_s[1] = cur_index;

    /* copy over values */
    for(var i = 0; i <= cur_index; i = i + 1;) {
      new_s[2 + i] = s[2 + i];
    }

    return new_s;
  }

  return s;
}

int get_val(int i) {
  /* turns a char_code i into a value v */
  return i - 48;
}

int int_of_string(string s) {
  var arr = array_of_string(s);
  var len = length_of_string(s);

  var sum = 0;
  for(var i = 0; i < len; i = i + 1;) {
    sum = sum * 10;
    var val = get_val(arr[i]);
    sum = sum + val;
  }

  return sum;
}



int program (int argc, string[] argv) {
  /* a stack based calculator. feed in input numbers and operands + and - */
  /* will calculate result. a reverse polish notation calculator */

  var str = "\n";

  var stack = new_stack();

  for(var i = 1; i < argc; i = i + 1;) {
    var current_item = argv[i];

    var did_op = false;

    var len = length_of_string(current_item);
    if(len == 1) {
      var arr = array_of_string(current_item);
      did_op = true;
      if(arr[0] == 43) {
        /* plus op */
        var x1 = peek_stack(stack);
        stack = pop_stack(stack);
        var x2 = peek_stack(stack);
        stack = pop_stack(stack);
        stack = push_stack(stack, x1 + x2);
      } else if(arr[0] == 45) {
        /* minus op */
        var x1 = peek_stack(stack);
        stack = pop_stack(stack);
        var x2 = peek_stack(stack);
        stack = pop_stack(stack);
        stack = push_stack(stack, x1 - x2);
      } else if(arr[0] == 120) {
        /* times op */
        var x1 = peek_stack(stack);
        stack = pop_stack(stack);
        var x2 = peek_stack(stack);
        stack = pop_stack(stack);
        stack = push_stack(stack, x1 * x2);
      } else {
        did_op = false;
      }
    }

    if(!did_op) {
      /* didn't do op! we have a number maybe */
      var v = int_of_string(current_item);
      stack = push_stack(stack, v);
    }
  }

  print_int(peek_stack(stack));
  return peek_stack(stack);
}