神之题解

#include<bits/stdc++.h>
using namespace std;
string s;
int f(int l, int r){
    if(l > r) return 0;
    string t = "";
    while(l <= r && s[l] >= 'A' && s[l] <= 'Z')
        t += s[l++];
    int m = 0;
    while(l <= r && s[l] >= '0' && s[l] <= '9')
        m = m * 10 + s[l++] - '0';
    if(t == "FD") return m + f(l, r);
    else if(t == "BK") return - m + f(l, r);
    else{
        int ans = 0;
        for(int i = l; i <= r; i++){
            if(s[i] == '[') ans++;
            if(s[i] == ']') ans--;
            if(ans == 0)
                return m * f(l+1, i-1) + f(i+1, r);
        }
    }
}
int main(){
	string str;
    while(cin >> str) s += str;
    cout << abs(f(0, s.size() - 1));
	return 0;
}