#include <iostream>
#include <stdio.h>
#include <bitset>
using namespace std;
FILE* f, * g;
bitset <2000002> v;
int main()
{
    int n, nr = 0, i, j;
    f = fopen("ciur.in", "r");
    g = fopen("ciur.out", "w");
    fscanf(f, "%d", &n);
    for (i = 2;i <= n;i++)
    {
        if (v[i] == 0)
        {
            nr++;
            for (j = i * 2;j <= n;j = j + i)
            {
                v[j] = 1;
            }

        }
    }

    fprintf(g, "%d", nr);
    fclose(f);
    fclose(g);
    return 0;
}