#include <stdio.h>

using namespace std;

FILE*f=fopen("ciur.in","r"),*g=fopen("ciur.out","w");
int n, v[2000100], sol;

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

int main()
{
    fscanf(f,"%d",&n);
    ciur();
    fprintf(g,"%d ",sol);
    return 0;
}