#include <stdio.h>
#include <math.h>
#define N 2000000
bool a[N+1];
int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,s=1;
    scanf("%i",&n);
    int sqrtn=sqrt(n);
    for(int i=3;i<=sqrtn;i+=2){
        if(!a[i]){
            int i2=i<<1;
            for(int j=i+i2;j<=n;j+=i2)a[j]=true;
            }
        }
    for(int i=3;i<=n;i+=2)s+=!a[i];
    printf("%i",s);
    return 0;
    }