Is there any specific math book or notes that I can solve to improve my programming skill.

Why i am getting memory limit exceeded

Problem 318A

include<bits/stdc++.h>

using namespace std;

int main() { long long n,j; cin>>n>>j;

vector<long long>v;

for(int i=1;i<=n;i+=2)
{
     v.push_back(i);
}

for(int j=2;j<=n;j+=2)
{
    v.push_back(j);
}

cout<<v[j-1]<<endl;

}