'''class Solution {
public:
int countElements(vector& arr) {
//int len = arr.size();
int count = 0;
map<int,int> m;
set s;
for(int x:arr){
s.insert(x);
}
for(int x:arr){
m[x]++;
}
for(auto x:s){
if(s.count(x)==1 && s.count(x+1)==1){
count = count+m[x];
}
}
return count;
}
};'''