#include <bits/stdc++.h>
using namespace std;
int q,n,cod,x,a[200005],nr,i,j,p[200005];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=3;i<=n;i=i+2)
    {
        if(p[i]==0)
        {
            nr++;
            if(i<1500)
            {
                for(j=i*i;j<=n;j=j+i)
                    p[j]=1;

            }
        }
    }
    nr++;
    printf("%d",nr);
    return 0;
}