/in/foo.c: In function 'main':
/in/foo.c:8:2: error: expected ';' before 'for'
  for(i=2;i<=n;i++)
  ^~~
/in/foo.c:5:13: warning: unused variable 'b' [-Wunused-variable]
  long n,i,a,b;
             ^
/in/foo.c:5:9: warning: unused variable 'i' [-Wunused-variable]
  long n,i,a,b;
         ^