/in/foo.cc: In function 'int main()':
/in/foo.cc:18:26: warning: operation on 'tot' may be undefined [-Wsequence-point]
  for(int i=1;i<=n;++i) s[++tot]=tot+2,s[++tot]=str[i]-'0';
                          ^~~~~
/in/foo.cc:19:4: warning: operation on 'tot' may be undefined [-Wsequence-point]
  s[++tot]=tot+2;
    ^~~~~
/in/foo.cc:22:44: warning: suggest parentheses around '-' inside '>>' [-Wparentheses]
  for(int i=1;i<=tot;++i) if(i&1) ans+=rl[i]-1>>1;
                                       ~~~~~^~