#include <iostream>

using namespace std;

int getPrime(int maxInt)
{
    if(maxInt == 1) return -1;
    int tmp = maxInt;
    bool flag = 0;
    while(!flag){
        if(tmp < 2) return -1;
        for(int i=2; i<maxInt; --i){
            if(tmp%maxInt) break;
            else flag = true;
        }
        --tmp;
    }
    return tmp;
}

int main()
{
    int N;
    cin >> N;
    int ans;
    while((N = getPrime(N)) != -1){
        ans +=N;
        N-=1;
    }
    cout << ans << endl;
    
    return 0;
}