#include <stdio.h>

using namespace std;

int n,s,v[2000000];
int main()
{freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d", &n);
for(int i=2;i<=n;i++)
    v[i]=1;
for(int i=2;i<=n;i++)
{
    if(v[i])
    {
        s++;
        for(int j=2*i;j<=n;j+=i)
            v[j]=0;
    }
}
printf("%d",s);
    return 0;
}