View Compilation Error

0_0_37058510_8406.cpp:2:11: error: '::main' must return 'int'
 void main()
           ^
0_0_37058510_8406.cpp: In function 'int main()':
0_0_37058510_8406.cpp:4:5: error: 'longlong' was not declared in this scope
     longlong n,i,a[100];
     ^
0_0_37058510_8406.cpp:5:25: error: 'n' was not declared in this scope
     while(scanf("%lld",&n)!=EOF)
                         ^
0_0_37058510_8406.cpp:7:9: error: 'a' was not declared in this scope
         a[2]=1;a[3]=2;
         ^
0_0_37058510_8406.cpp:10:17: error: 'i' was not declared in this scope
             for(i=4;i<=n;i++)
                 ^
0_0_37058510_8406.cpp:17:5: error: return-statement with no value, in function returning 'int' [-fpermissive]
     return ;
     ^