#include<iostream>
int n,c;
bool a[2000001];
void ciur(){
    for(int i=2;i<=n;i++){
        if(!a[i]){
            c++;
            for(int j=2*i;j<=n;j+=i){
                a[j]=1;
            }
        }
    }
}
int main(){
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d",&n);
    ciur();
    printf("%d",c);