#include<stdio.h>
int N, c;
char prim[2000005];
int main() {
    int i, j;
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d", &N);
    for (i = 2; i <= N; i++) {
        prim[i] = 1;
    }
    for (i = 2; i <= N; i++) {
        if (prim[i]) {
            ++c;
            for (j = i * 2; j <= N; j += i) {
                prim[j] = 0;
            }
        }
    }
    printf("%d", c);
    return 0;
}