STL vector

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#include<iostream>#include<cstdio>#include<algorithm>#include<vector>using namespace std;//using std::vector;vector<int>a(1);int main(){int n,x,m;cin>>n;for(int i=1;i<=n;i++){cin>>x;a.push_back(x);}cout<<a.size();cin>>m;cout<<a.at(m)<<endl;cout<<"first"<<a.front()<<endl;cout<<"last"<<a.back(); }