#include stdio.h
 
int N, cnt;
char prim[2000005];
 
int main(void)
{
    int i, j;
     
    freopen(ciur.in, r, stdin);
    freopen(ciur.out, w, stdout);
 
    scanf(%d, &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;
        }
 
    printf(%dn, cnt);
 
    return 0;
}