#include <fstream.h>
int N, cnt;
char prim[2000005];
int main()
{
    int i, j;
    ifstream F("ciur.in");
    ofstream g("ciur.out");
    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;
    return 0;
}