#include <cstdio>

using namespace std;

char ciur[2000005];

int main(){
    int n, i, j, ans;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &n);
    for (i=2; i*i<=n; i++)
        if (!ciur[i])
            for (j=i*i; j<=n; j+=i)
                ciur[j]=1;
    ans=0;
    for (i=2; i<=n; i++)
        if (!ciur[i]) ans++;
    printf("%d\n", ans);
    return 0;
}