#include<cstdio>

using namespace std;

bool ciur[2000001];

int main()
{
    FILE *f, *g;
    int n, i, j, rez = 0;

    f=fopen("ciur.in", "r");

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

    fclose(f);

    for(i = 2; i <= n; ++i)
        if(!ciur[i])
        {
            ++rez;
            for(j = i * i; j <= n; j += i)
                ciur[j] = true;
        }

    g=fopen("ciur.out", "w");

    fprintf(g, "%i", rez);

    fclose(g);

    return 0;
}