Codeforces Round #207 (Div. 2) A. Group of Students

 #include <iostream>
 #include <vector>

 using namespace std;

 int main(){
     int m,sum = ;
     cin >> m ;
     vector<int> c(m+,);
     for(int i = ; i <= m ; ++ i) {cin >> c[i];sum+=c[i];}
     int x,y,firstPart = , secondPart = ,firstIndex = , secondIndex =;
     cin >>  x >>  y;
     for(firstIndex = ,secondIndex = m+;firstIndex < secondIndex;){
         if (firstPart < x) firstPart+=c[++firstIndex];
         if (secondPart < x) secondPart += c[--secondIndex];
         if( firstPart >= x && secondPart >= x ) break;
     }
     if(firstPart > y || secondPart > y) cout<<<<endl;
     else{
         if(firstIndex >= secondIndex) cout<<<<endl;
         else{
             if(sum - firstPart - secondPart > *(y-x)) cout<<<<endl;
             else{
                 while(secondPart + c[secondIndex-]<= y && (secondIndex-) > firstIndex){
                     secondIndex--;
                     secondPart+=c[secondIndex];
                 }
                 if (secondIndex- <= firstIndex) cout<<secondIndex<<endl;
                 else{
                     if(sum - secondPart > y) cout<<<<endl;
                     else cout<<secondIndex<<endl;
                 }
             }
         }
     }
 }