#include <cstdio>

using namespace std;

FILE *fin, *fout;

int main()
{
    fin = fopen("ciur.in", "r");
    fout = fopen("ciur.out", "w");

    int n, rez = 0;
    bool P[2000000] = {0};

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

    for(int i = 2; i <= n; i++)
    {
        if(!P[i])
        {
            rez++;
            for(int j = i+i; j <= n; j+=i)
                P[j] = 1;
        }
    }

    fprintf(fout, "%d\n", rez);
    fclose(fin);
    fclose(fout);



    return 0;
}