#include <cstdio>
#define NMAX 2000000

FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
int v[NMAX];
int cnt;
void ciur(int n)
{
    int i,j;

    for(i=2; i<=n; i++)
        if(v[i]==0)
        {
               cnt++;
               for(j=i+i; j<=n; j+=i)
                    v[j]=1;

        }


}

int main()
{
    int n,i,k=0;
    fscanf(f,"%d",&n);


    ciur(n);

    fprintf(g,"%d", cnt);
    return 0;
}