#include<cstdio>

using namespace std;

int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    nr=0;
    for(i=2;i<=n;i++){
        prim=true;
        for(j=2;j*j<=i;j++){
            if(i%j==0)
            {
                prim=false;
                break;
            }
        }
        if(prim)nr++;
    }
    printf("%d",nr);
    return 0;
}