| Year | Value | | 2021 | 340.52324357507 | | 2020 | 475.7180842333 | | 2019 | 468.40350576256 | | 2018 | 466.57060161644 | | 2017 | 497.40602869912 | | 2016 | 484.89058972919 | | 2015 | 548.96845448492 | | 2014 | 575.91681542361 | | 2013 | 597.35615804387 | | 2012 | 605.7520036626 | | 2011 | 566.66810049764 | | 2010 | 505.23019262694 | | 2009 | 403.41118349652 | | 1981 | 272.9789920942 | | 1980 | 257.82263205199 | | 1979 | 253.88057174931 | | 1978 | 227.63831059561 | | 1977 | 207.42704989353 | | 1976 | 183.12531637159 |
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