#include <cstdio>
#include <bitset>
using namespace std;

bitset <2000005> Q;

int main()
{

    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);

    int n, i, j, s;
    s = 0;

    scanf("%d",&n);

    for( i = 2; i <= n; ++i ){
        if( !Q[i] ){
            s++;
            for( j = i; j <= n; j += i ) Q[j] = true;
        }
    }

    printf("%d",s);


    return 0;
}