View Compilation Error

0_0_28127834_15942.cpp: In function 'int main()':
0_0_28127834_15942.cpp:23:5: error: redefinition of 'int main()'
 int main()
     ^
0_0_28127834_15942.cpp:2:5: note: 'int main()' previously defined here
 int main()             //即为  （首项+首项+（项数-1）*公差）/2 = 首项+（项数-1）*公差/2
     ^