#include<fstream.h>
ifstream f("ciur.in");
ofstream g("ciur.out");
int N, cnt;
char prim[2000005];
int main(void)
{
    int i, j;
    f>>N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }
    g<<cnt;
    f.close();
    g.close();
    return 0;
}