def METHOD_NAME(df: pd.DataFrame) -> pd.DataFrame:
    id_vars = ["country", "year"]
    var_name = "chemical"
    value_name = "consumption"
    df = df.pivot(index=id_vars, columns=[var_name], values=value_name).reset_index()
    df = df.melt(id_vars=id_vars, var_name=var_name, value_name=value_name)
    df["consumption_zf"] = df["consumption"].fillna(0)
    return df