#include <cstdio>

using namespace std;

bool v[2000001];

int main()
{
    FILE *f = fopen("ciur.in","r");
    FILE *g = fopen("ciur.out","w");

    int n,rez=0;
    fscanf(f,"%d",&n);
    for(int i=2;i<=n;i++)
    {
        if(v[i] == false)
        {
            rez++;
            for(int j=i*2;j<=n;j=j+i)
                v[j] = true;
        }
    }
    fprintf(g,"%d",rez);
    return 0;
}