memset(cnt,0,sizeof(cnt));

if(S[0]=='['){

cnt[0] = 1;

}

for(int i=1; i<S.size(); i++){

if(S[i]=='['){

cnt[i] = cnt[i-1]+1;

}else{

cnt[i] = cnt[i-1];

}

}

pre();

stack< pcc > my_stack;

memset(rec,-1,sizeof(rec));

for(int i=0; i<S.size(); i++){

if(my_stack.empty()){

my_stack.push( pcc(S[i], i) );

}else{

char top = my_stack.top().first;

char now = S[i];

if((top=='(' && now==')') || (top=='[' && now==']') ){

rec[my_stack.top().second] = i;

my_stack.pop();

}else if((top=='(' && now==']') && (top=='['&&now==')')) {

while(!my_stack.empty()){

my_stack.pop();

}

}else{

my_stack.push( pcc(S[i],i));

}

}

}

/*

sz = S.size();

int ans = -1;

int ans_left, ans_right;

int cur = 0;

string t_str, ans_str;

while(1){

//cout<<"cur at "<<cur<<endl;

if(cur>=sz)break;

if(rec[cur]!=-1){

t_str += S.substr(cur, rec[cur]-cur+1);

cur = rec[cur]+1;

int cnt =0;

for(int k=0; k<t_str.size(); k++){

if(t_str[k]=='['){

cnt++;

}

}

if(cnt>ans){

ans = cnt;

ans_str = t_str;

}

}else{

t_str = "";

cur++;

}

}

if(ans==-1){

cout<<0<<endl;

}else{

cout<<ans<<endl;

cout<<ans_str<<endl;

}

cin>>S;

work();

return 0;