#include <cstdio>
#define LIM 2000000

using namespace std;

int p[LIM+10];
void ciur()
{
    int i,j,k=-1;
    for(i=2;i<=LIM;++i)
        if(p[i]==0)
        {
            k++;
            p[k]=i;
            for(j=i+i;j<=LIM;j=j+i)
                p[j]=1;
        }
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int n,rasp=0;
    scanf("%d",&n);
    ciur();
    for(int i=0;p[i]<=n;++i)
        rasp++;
    printf("%d",rasp);
    return 0;
}