#include <stdio.h>
#include <math.h>

using namespace std;

FILE*f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
int n, sol;
bool v[2000009];

void ciur()
{
    for(int i = 2; i < sqrt(n); i++)
    {
        if(v[i] == 0)
        {
            int j = 2*i;
            while(j < n)
                v[j] = 1, j += i;
        }
    }
}

int main()
{
    fscanf(f,"%d",&n);
    ciur();
    for(int i = 2; i < n; i++)
        if(v[i] == 0) sol++;
    fprintf(g,"%d ",sol);
    return 0;
}