#include <cstdio>
#include <bitset>
#include <cmath>

using namespace std;

int main()
{
    FILE * iFile;
    FILE * oFile;

    iFile = fopen("ciur.in", "r");
    oFile = fopen("ciur.out", "w");

    long n, i, j, count;
    bitset<20000000> nums;

    fscanf(iFile, "%ld", &n);
    count = n-1;

    for(i=2;i<=sqrt(n);i++)
    {
        if(nums[i] == 0)
        {
            for(j=i+i;j<=n;j=j+i)
            {
                if(nums[j] == 0)
                {
                    //nums[j] = 1;
                    count--;
                }
            }
        }
    }

    fprintf(oFile, "%ld", count);

    fclose(iFile);
    fclose(oFile);

    return 0;
}