#include <cstdio>

#define MAX  1 << 30

unsigned char V[MAX];

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

    int N, i, j, rez = 0;

    scanf("%d", &N);

    for (i = 3; i <= N; i += 2)
    {
        if (V[i >> 3] & (1 << (i & 7))) continue;
        ++rez;

       for (j = i * i ; j <= N && i<=1970; j += (i << 1) )
            V[j >> 3] |= (1 << (j & 7));
    }

    printf("%d\n", ++rez);

    return 0;
}