#include<cstdio>
#define NMAX 2000002
using namespace std;

int n, nr;
bool prim[NMAX];

int main()
{
    int i, j;
    FILE *fin = fopen("ciur.in","r");
    FILE *fout = fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    fclose(fin);
    prim[1] = 1;
    for(i=2; i*i<=n; i++)
        if(!prim[i])
            for(j=i*i; j<=n; j+=i)
                prim[j] = 1;
    for(i=1; i<=n; i++)
       if(!prim[i]) nr++;
    fprintf(fout,"%d\n",nr);
    fclose(fout);
    return 0;
}