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B=$\frac{1}{334 \times 1000}+\frac{1}{335\times 999}+\frac{1}{336\times 998}+...+\frac{1}{367\times 367} ...+\frac{1}{336\times 998}+\frac{1}{335\times 999}+\frac{1}{1000\times 334}$


B=$2 [\frac{1}{334 \times 1000}+\frac{1}{335\times 999}+\frac{1}{336\times 998}+...+\frac{1}{667\times 667}] - \frac{1}{667\times 667}$


1334 B= $2[\frac{1334}{334 \times 1000}+\frac{1334}{335\times 999}+\frac{1334}{336\times 998}+...+\frac{1334}{667\times 667}] - \frac{1334}{667\times 667}$

1334 B=$2[\frac{1}{334}+\frac{1}{1000}+\frac{1}{335}+\frac{1}{999}+...+\frac{1}{667}+\frac{1}{667}] - [\frac{1}{667}+\frac{1}{667}]$

1334 B=$2[\frac{1}{334}+\frac{1}{335}+\frac{1}{336}+...+\frac{1}{667}+...+\frac{1}{1000}]$

667 B=$\frac{1}{334}+\frac{1}{335}+\frac{1}{336}+...+\frac{1}{667}+...+\frac{1}{1000}$