string fairRations(vector B) { string ans; int cnt=0; int n=B.size();

for (int i=0;i<n;i++){
    if(i==n-1 && B[i]%2!=0){
        ans="NO";
        return ans;


    }
    if(B[i]%2!=0){

       B[i]++;
       B[i+1]++;
       cnt+=2;

    }
}
ans=to_string(cnt);
return ans; ;

}