foo.cc:24:5: error: redefinition of ‘int n’
   24 | int n,a[1001][1001],f[1001][1001];
      |     ^
foo.cc:3:5: note: ‘int n’ previously declared here
    3 | int n,a[1001][1001],f[1001][1001];
      |     ^
foo.cc:24:7: error: redefinition of ‘int a [1001][1001]’
   24 | int n,a[1001][1001],f[1001][1001];
      |       ^
foo.cc:3:7: note: ‘int a [1001][1001]’ previously declared here
    3 | int n,a[1001][1001],f[1001][1001];
      |       ^
foo.cc:24:21: error: redefinition of ‘int f [1001][1001]’
   24 | int n,a[1001][1001],f[1001][1001];
      |                     ^
foo.cc:3:21: note: ‘int f [1001][1001]’ previously declared here
    3 | int n,a[1001][1001],f[1001][1001];
      |                     ^
foo.cc:25:5: error: redefinition of ‘int main()’
   25 | int main(){
      |     ^~~~
foo.cc:4:5: note: ‘int main()’ previously defined here
    4 | int main(){
      |     ^~~~