foo.cc: In function 'void init_st()':
foo.cc:70:63: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
   70 |             st[i][len] = max(st[i][len - 1], st[i + (1 << len - 1)][len - 1]);
      |                                                           ~~~~^~~

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