#include<cstdio>
#include<cstring>
using namespace std;
int i, n, nr, y;
bool prim[2000005];
int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d", &n); nr=0;
    memset(prim, true, sizeof(prim));
    for (i=2;i<=n;i++) if (prim[i]==true) {
        nr++;
        y=i;
        while (y<=n) {y=y+i; prim[y]=false;}
    }
    printf("%d\n", nr); return 0;
}