#include <cstdio>

using namespace std;

char vaz[2000010];

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,r=0,j;
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
        if(vaz[i]==0)
        {
            r++;
            if(1LL*i*i<=n)
                for(int j=i*i;j<=n;j+=i) vaz[j]=1;
        }
    printf("%d",r);
    return 0;
}