#include <stdio.h>

int main(void) {

    int i, j, n, count;
    char prim[2000005];

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

    scanf("%d", &n);

    for(j = 2; j <= n; ++j)
        prim[j] = 1;

    for(j = 2; j <= n; ++i)
        if(prim[j]) {

            ++count;
            for(i = j + j; i <= n; i += j)
                prim[i] = 0;
        }

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

    return 0;
}