#include <cstdio>

using namespace std;

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

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++)
        if(!ciur[i])
    {
        s++;
        for(d=i+i;d<=n;d+=i)
            ciur[d]=1;
    }

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