Sum Numbers

In a given text you need to sum the numbers. Only separated numbers should be counted. If a number is part of a word it shouldn't be counted.

The text consists from numbers, spaces and english letters

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Input:
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A string.

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Output:
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An int.

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Example:
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sum_numbers('hi') == 0 sum_numbers('who is 1st here') == 0 sum_numbers('my numbers is 2') == 2 sum_numbers('This picture is an oil on canvas ' 'painting by Danish artist Anna ' 'Petersen between 1845 and 1910 year') == 3755 sum_numbers('5 plus 6 is') == 11 sum_numbers('') == 0