#include <bits/stdc++.h>

#define MAXN    2000005
#define INF     2e9

#define FILENAME    std::string("ciur")
std::ifstream input (FILENAME+".in");
std::ofstream output(FILENAME+".out");

int N;
bool ers[MAXN];

int main()
{
    input >> N;
    int cnt = 0;
    for (int i=2; i<=N; ++i) if (!ers[i]) {
        ++ cnt;
        for (int j=2*i; j<=N; j+=i)
            ers[j] = true;
    }   output << cnt << '\n';

    return 0;
}