#include <cstdio>

using namespace std;
int prim(int x)
{
    if(x < 2 || x > 2 && x%2==0)
        return 0;
    for(int d=3;d*d<=x;d+=2)
        if(x%d==0)
            return 0;
    return 1;
}
int n;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    int nr=0;
    for(int i=2;i<=n;i++)
    {
        if(prim(i)==1)
            nr++;
    }
    printf("%d\n",nr);
    return 0;
}