#include<cstdio>
#define N_MAX 2000000
using namespace std;

bool ciur[N_MAX+1];
int n, nr;

void ciurul()
{
    int d, i;
    for(d=2; d<=n; d++)
        if(!ciur[d])
        {
            nr++;
            for(i=2*d; i<=n; i+=d)
                ciur[i] = 1;
        }
}

int main()
{
    FILE *fin, *fout;
    fin = fopen("ciur.in","r");
    fout = fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    ciurul();
    fprintf(fout,"%d\n",nr);
    fclose(fin);
    fclose(fout);
    return 0;
}