#include <stdio.h>

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