#include <stdio.h>
#include <string.h>

char ciur[2000001];
int main () {
    FILE *fin=fopen ("ciur.in", "r"),
         *fout=fopen ("ciur.out", "w");
    memset(ciur, 1, sizeof ciur);

    int n, i, d, ct;
    fscanf (fin, "%d", &n);
    ct=n>1;
    for (i=3; i<=n; i+=2)
        if (ciur[i])
            for (++ct, d=i<<1; d<=n; d+=i)
                ciur[d]=0;
    fprintf (fout, "%d\n", ct);
    return 0;
}