#include <fstream>
#include <vector>
#define N 2000001
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int n;
bool ciur[N];
vector<int> prime;

int main()
{
    in>>n;

    for(int i = 2; i <= N; ++i)
        if(!ciur[i]){
            prime.push_back(i);
            for(int j = i + i; j <= N ; j += i)
                ciur[j] = 1;
        }

    int i = 0;
    while(prime[i] <= n) i++;

    out<<i;

    in.close();
    out.close();
    return 0;
}