1 #include<cstdio>
 2 #include<cstring>
 3 const int M=16;
 4 char s[M],cp[M][M]={"A","A-","B+","B","B-","C+","C","C-","D","D-","F"};
 5 double si[]={4,3.7,3.3,3,2.7,2.3,2,1.7,1.3,1.0,0};
 6 int main(){
 7     int n;
 8     while(~scanf("%d",&n)){
 9         double ss=0;
10         int sc=0,c;
11         while(n--){
12             scanf("%d%s",&c,s);
13             for(int i=0;i<11;i++){
14                 if(!strcmp(cp[i],s)){
15                     ss+=si[i]*c;
16                     sc+=c;
17                     break;
18                 }
19             }
20         }
21         if(!sc){
22             puts("0.00");
23             continue;
24         }
25         printf("%.2f\n",ss/sc);
26     }
27     return 0;
28 }