#include <cstdio>

using namespace std;
FILE* FIN=freopen("ciur.in","r",stdin);
FILE* FOUT=freopen("ciur.out","w",stdout);

bool v[2000001];
int n,sol;

void eratostene()
{
    int p,i;
    for(p=4;p<=n;p+=2)
        v[p]=1;
    sol++;
    for(i=3;i<=n;i+=2)
        if(!v[i])
        {
            if(i<2000)
                for(p=i*i;p<=n;p+=i+i)
                    v[p]=1;
            sol++;
        }
}
int main()
{
    scanf("%d",&n);
    eratostene();
    printf("%d",sol);
    return 0;
}