#include <stdio.h>

bool aparitii[2000005];

int main()
{
    FILE *in, *out;
    in = fopen("ciur.in", "r");
    out = fopen("ciur.out", "w");
    int n;
    fscanf(in, "%d", &n);
    int ct = 0;
    for (int i = 2; i <= n; i++)
    {
        if(aparitii[i]==0)
        {
            //fprintf(out, "%d ", i);
            ct++;
            for (int j = 2 * i; j <= n; j = j + i)
                aparitii[j] = 1;
        }
    }
    fprintf(out, "%d\n", ct);
    fclose(in);
    fclose(out);
    return 0;
}