#include<stdio.h>   
int main()   
{   
    int n,i,j,nr=0;   
    bool a[2000001];   
    freopen("ciur.in","r",stdin);   
    freopen("ciur.out","w",stdout);   
    scanf("%d",&n);   
    for(i=2;i<=n;i++)   
        a[i]=true;   
    for(i=2;i*i<=n;i++)   
        if(a[i])   
            for(j=i*i;j<=n;j=j+i)   
                a[j]=false;   
    for(i=2;i<=n;i++)   
        if(a[i]) nr++;   
    printf("%d",nr);   
        return 0;   
}