#include<bits/stdc++.h>
int main()
{
    long long int low, high, i, flag,c, s ;
    while(scanf("%lld",  &high)!=EOF){
    long long int start = 2;

    c = 0;


    while (start <= high)
    {
        flag = 0;
        s = sqrt(start);
        for(i = 2; i <= s; i++)
        {
            if(start% i == 0)
            {
                flag = 1;
                break;
            }
        }

        if (flag == 0)
        {
              c++;
        }
        start++;

    }
    printf("%lld\n",c);

    }