#!/bin/awk -f

function push(x) { stack[++sp] = x; }
function pop() { if(sp > 0) sp--; else err = "Stack underflow"; }
function top(){ if(sp > 0) print stack[sp]; }

function eval(x) {
  if(x != "-" && (x ~ /^[-.0-9][0-9]*[.0-9]?[0-9]*$/)) push(x);
  else {
    second = stack[sp]; pop();
    first = stack[sp];  pop();
    if(x == "+") push(first + second);
    else if(x == "-") push(first - second);
    else if(x == "*") push(first * second);
    else if(x == "/") push(first / second);
    else err = "Bad operator: " + x;
  }
}

BEGIN { sp = 0; }

{
  err = "";
  for(i = 1; i <= NF; i++) { eval($i); if(err) break; }
  if(!err) top();
  else print "Error:", err;
}