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

bool viz[nmx];

int main() {
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);

    int nr,sum = 0;
    scanf("%d", &nr);

    for(int i = 2; i <= nr; ++i)
        if(not viz[i]) {
            ++sum;
            for(int j = 2*i; j <= nr; j += i)
                viz[j] = 1;
        }

    printf("%d\n", sum);

    return 0;
}