/in/foo.cc: In function 'int main()':
/in/foo.cc:21:23: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   if(f[f[i][0]][0]!=i && f[f[i][0]][1]!=i || f[f[i][1]][1]!=i && f[f[i][1]][0]!=i )
      ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~