#include <iostream>

using namespace std;

int E[2000000];
int main()
{
    int n, i, j, c = 0;

    FILE *in, *out;
    in = fopen("ciur.in", "r");
    out= fopen ("ciur.out", "w");
    fscanf(in, "%d", &n);
    for(i = 2; i * i <= n; i++)
    {
        if(E[i] == 0)
        {
            for(j = i*i; j <= n; j += i)
                E[j] = 1;
        }
    }

    for(i = 2; i <= n; i++)
    {
        if(E[i]==0)
            c++;

    }
    fprintf(out, "%d", c);

    return 0;
}