#include <stdio.h>
int n,nr;
bool v[2000000];
void ciur(){
    int i,m;
    v[0]=1;
    v[1]=1;
    for (i=2;i<=n;++i){
        if (v[i]==0){
            m=0;
            for (m=i+i;m<=n;m+=i)
                v[m]=1;
        }
    }
    for (i=1;i<=n;++i)
        if (v[i]==0)
            ++nr;
    return;
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    ciur();
    printf("%d",nr);
	return 0;
}