Simple calculation of mathematical problems! 1+2-3-4+5+6-7-8+9+10-11-12…… -1999-2000+2001+2002-2003-2004+2005+2006 Also, simple calculation: 222222 * 5555

1+2-3-4+5+6-7-8+9+10-11-12…… -1999-2000+2001+2002-2003-2004+2005+2006
Head to tail correspondence addition
＝[(1+2006)+(2+2005)-(3+2004)-(4+2003)]+...+[(1001+1006)+(1002+1005)-(1003+1004)]
＝0+2007
＝2007

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