#include<stdio.h>

int main()
{
    FILE* fr = fopen("ciur.in", "r");
    FILE* fw = fopen("ciur.out", "w");
    int n;
    fscanf(fr, "%d", &n);
    char *A = new char[n+1];
    for(int i = 0; i <= n; i++)
        A[i] = 0;
    A[1] = 1;
    for(int i = 2; i <= n; i++)
        if(A[i] == 0)
           for(int j = i * 2; j <= n; j+=i)
                A[j] = 1;

    int k = 0;
    for(int i = 1; i <= n; i++)
        if(A[i] == 0)
            k++;
    fprintf(fw, "%d", k);
    return 0;
}