foo.cc: In function 'int main()':
foo.cc:10:15: warning: iteration 3 invokes undefined behavior [-Waggressive-loop-optimizations]
   10 |    sum+=s[i][j];
      |         ~~~~~~^
foo.cc:8:16: note: within this loop
    8 |   for(int j=1;j<=4;j++){
      |               ~^~~

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