import java.util.Deque;
import java.util.HashMap;

class TreeNode {
}

class SymbolTableEntry<K extends TreeNode, V extends TreeNode> {
}

class AbstractSymbol {
}

class NoScopePresentException extends Exception {
}

public class Test {
    private Deque<HashMap<AbstractSymbol, SymbolTableEntry<? extends TreeNode, ? extends TreeNode>>> st;

    public SymbolTableEntry<? extends TreeNode, ? extends TreeNode> lookup(AbstractSymbol sym) throws NoScopePresentException
    {

        for(HashMap<AbstractSymbol, SymbolTableEntry<? extends TreeNode, ? extends TreeNode>> node : st) {
            if (node.containsKey(sym))
                return node.get(sym);
        }
        return null;
    }
}