#include <iostream>
#include <cstring>
using namespace std;
char str[1000100];
int main(){
	int n;
	cin>>n>>str;
	int an=0;
	for(int i=0;i<n;i++){
		if(str[i]>='a'&&str[i]<='z')an+=str[i]-'a'+1;
		if(str[i]>='A'&&str[i]<='Z')an-=str[i];
	}
	cout<<an<<endl;
	return 0;
}