The episode demonstrated to both Scotland and England the fruitlessness of their struggles. Thereafter, with France's fortunes falling and England's rising, the terms came to seem more favourable to the Scots, and in 1357 they were accepted after all, formalized in the Treaty of Berwick, under the terms of which Scotland would pay England 100,000 merks over a ten-year period. With the signing of the Treaty of Berwick, the Second War of Scottish Independence was effectively over. Even before the signing of the treaty, in January 1356, Edward Balliol — weary and ill — had relinquished his claim in the kingdom of Scotland to Edward III in exchange for an annuity of £2000. He retired to live the rest of his life in the area of Yorkshire. David II returned to Scotland, to try again to deal with the rivalries of his lords as well as now among his ladies, as his wife Joan evidently objected to the English mistress he had taken during his 11 years in captivity. The treaty did impose a financial hardship on Scotland, but David II stopped paying after only 20,000 merks of the debt had been met, following which renegotiation led ultimately to a reduction in the debt and a 14-year truce.

Answer this question based on the article: How many years was the truce David II agreed to after only paying 20000 merks?
14