PROGRAMMING:π/ 4 ≈ 1-1 / 3 + 1 / 5 π

Use the formula π/ 4 ≈ 1-1 / 3 + 1 / 5 π Until the absolute value of the last term is less than 0.00000 1.
###Output format:
According to the order of "pi = result", the format width of the result output is 10 columns, and 4 decimal places are reserved.
###Output example:
```out
pi= 3.1416
```






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