def build_structure(departments, ages):
    """Builds the skeleton of the data."""
    accounts = dict()
    
    for department in departments:
        accounts.update({
            department: {
                age: {
                    "n_tot_dose1": int(),
                    "n_tot_complet": int(),
                    "rate_dose1": float(),
                    "rate_complet": float(),
                }
                for age in ages
            }
        })

    return accounts