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//http://blog.miskcoo.com/2015/04/bzoj-4001
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#include <cstdio>
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int main()
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{
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int n;
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scanf("%d", &n);
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printf("%.9lf", 1.0 * n * (n + 1) / 2 / (n * 2 - 1));
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return 0;
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} |
