#include <cstdio>

using namespace std;

int ciur[2000005];
int n,s=0;

int main()
{
    int i,d;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);

    for(int i=2;i<=n;++i)
        ciur[i]=1;

    for(i=2; i<=n; ++i)
        if(ciur[i])
        {
            ++s;
            for(d=i+i; d<=n; d+=i)
                ciur[d]=0;
        }

    printf("%d\n",s);
    return 0;
}