#include <cstdio>
#include <math.h>

using namespace std;

int ciur[2000005];

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