#include<cstdio>
#include<vector>
using namespace std;
vector <int> prime;
int low[2000001];
int main(){
    int i,j,n;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++){
        if(low[i]==0){
            low[i]=i;
            prime.push_back(i);
        }
        for(j=0;j<prime.size()&&prime[j]<=low[i]&&prime[j]*i<=n;j++)
            low[prime[j]*i]=prime[j];
    }
    printf("%d",prime.size());
    return 0;
}