# include <cstdio>
    using namespace std;

    int n,nr;
    bool w[2000004];

    void ciur(int k)
    {
        for(int i=2; i<=k; ++i)
            w[i]=1;
        for(int i=2; i<=k; ++i)
            if(w[i])
            {
                ++nr;
                for(int j=i+i; j<=k; j=j+i)
                    w[j]=0;
            }
    }

    int main()
    {
        FILE * f = fopen ("ciur.in","r");
        FILE * g = fopen ("ciur.out","w");

        fscanf(f,"%d", &n);

        ciur(n);

        fprintf(g,"%d\n",nr);

        return 0;

    }