#include <cstdio>
#include <vector>
#define MAX_N 2000000

using namespace std;

long N;

void ciur()
{
    vector <bool> V(MAX_N,0);
    int cnt = 0;

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

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