#include<bits/stdc++.h>
using namespace std;
int read(){
    int x=0,f=1;
    char ch=getchar();
    while(ch<'0' || ch>'9'){ if(ch=='-') f=-1;ch=getchar();}
    while(ch>='0' && ch<='9'){x=(x<<3)+(x<<1)+(ch^48);ch=getchar();}
    return x*f;
}
long long f(){
	long long sum=0,x;
	char a;
	while(1){
		a=getchar();
		if(a=='F') {
			x=2;
			while(x--) getchar();
			x=read();
			sum+=x;
		}
		else if(a=='B'){
			x=2;
			while(x--) getchar();
			x=read();
			sum-=x;
		}
		else if(a=='R'){
			x=6;
			while(x--) getchar();
			x=read();
			sum+=x*(f());
		}
		else return sum;
	}
	return sum;
}
int main(){
	cout<<abs(f());
	return 0;
}