#include<bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint=modint998244353;
using namespace std;
using ll=long long;
using ul=unsigned long long;
int dx[8] = {-1, 1, 0, 0, -1, -1, 1, 1};
int dy[8] = {0, 0, -1, 1, -1, 1, -1, 1};
using Graph=vector<vector<int>>;
int main(){
    int N;
    cin>>N;
    vector<bool>A(N+1);
    vector<int>E;
    for(int i=2;i<=N;i++){
        if(A[i])continue;
        E.push_back(i);
        for(int j=i*2;j<=N;j+=i)A[j]=true;
    }
    cout<<accumulate(E.begin(),E.end(),0)<<endl;
}