#include <stdio.h>

using namespace std;
const int N = 2000005;
bool v[N];
int main()
{
    FILE *in, *out;
    in = fopen("ciur.in", "r");
    out = fopen("ciur.out", "w");
    int n;
    fscanf(in, "%d", &n);
    int cont=0;
    for(int i=2; i<=n; i++)
    {
        if(v[i]==false)
        {

            for(int j=i+i; j<=n; j+=i){
                v[j]=true;
            }
            cont++;
        }
    }
    fprintf(out, "%d", cont);
    return 0;
}