#include <stdio.h>

int Ciur[2000005];

int main()
{
    int N, i, j, numar = 0;

    FILE *input = fopen("ciur.in", "r");
    FILE *output = fopen("ciur.out", "w");
    fscanf(input, "%d", &N);

    for (i = 2; i <= N; ++i) Ciur[i] = 1;

    for (i = 2; i <= N; ++i)
    if (Ciur[i])
    {
        ++numar;
        for (j = i + i; j <= N; j += i)
            Ciur[j] = 0;
    }

    fprintf(output, "%d", numar);

    return 0;
}