#include <bits/stdc++.h>

#define MaxN 2000005

std::ifstream InFile("ciur.in");
std::ofstream OutFile("ciur.out");

int N;
bool Sieve[MaxN];

int main()
{
    InFile >> N;

    int Cnt = 0;
    for (int i=2, j; i<N; ++i)
        if (Sieve[i] == 0) {
            ++Cnt;

            for (j=2*i; j<N; j+=i)
                Sieve[j] = 1;
        }

    OutFile << Cnt << '\n';

    return 0;
}