#include <cstdio>
#include <vector>
#define MAX_N 2000001

using namespace std;

long long N;

void ciur()
{
    long cnt = 0;
    vector <bool> V(N+1);

    for(long i=2; i<=N; i++)
    {
        if(V[i]) continue;
        V[i] = 1;
        for(long j=i; (long long)i*j <= N; j++)
                V[i*j] = 1;
        ++ cnt;
    }
    printf("%ld\n",cnt);
}

int main()
{
    freopen("ciur.in","rt",stdin);
    freopen("ciur.out","wt",stdout);
    scanf("%lld",&N);
    ciur();
}