#include <bits/stdc++.h>

using namespace std;

FILE *F=fopen("ciur.in", "r"), *G=fopen("ciur.out", "w");

int n, a[2000005], k;

int main()
{
    fscanf(F, "%d", &n);
    for(int i = 2; i <= n/2; ++ i)
        if(!a[i])
            for(int j = i+i; j <= n; j += i)
                a[j] = 1;
    for(int i = 2; i <= n; ++ i)
        if(!a[i]) k++;
    fprintf(G, "%d", k);
    return 0;
}