# include <cstdio>
# define N (1<<21)

using namespace std;

bool prim[N];
int nr;

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    int n; scanf("%d\n", & n);
    for(int i=2; i<=n; ++i) prim[i]=1;
    for(int i=2; i<=n; ++i)
        if(prim[i])
        {
            nr++;
            for(int j=2*i; j<=n; j+=i)
                prim[j]=0;
        }
    printf("%d\n", nr);
}