#include <stdio.h>
#include <stdlib.h>

int main()
{

const int NMAX = 1 << 17;

unsigned char V[NMAX];
    FILE *f,*g;
    f=fopen("ciur.in", "rt");
    g=fopen("ciur.out", "wt");
    int N, i, j, i2, nrprime = 0;

    scanf("%d", &N);

    for (i = 3; i <= N; i += 2) {
        if (V[i >> 4] & (1 << ((i >> 1) & 7))) continue;
        ++nrprime;

        for (j = i + (i2 = i + i); j <= N; j += i2)
            V[j >> 4] |= 1 << ((j >> 1) & 7);
    }

    printf("%d\n", nrprime + 1);

    return 0;
}