#include <cstdio>
#include <algorithm>
#include <vector>

#define in "ciur.in"
#define out "ciur.out"
#define NMAX (2000000 + 7)
#define LL long long

using namespace std;
LL n, cnt = 1;
bool ciur[NMAX];

int main()
{
    freopen(in, "ciur.in", stdin);
    freopen(out, "ciur.out", stdout);
    scanf("%lld", &n);
    ciur[1] = 1;
    for(LL i = 4; i<= n; i+=2) ciur[i] = 1;
    for(LL i = 3; i<= n; i+=2)
    {
        if(ciur[i]) continue;
        cnt ++;
        for(LL j = 1LL*i*i; j<= n; j+=i)
        {
            ciur[j] = 1;
        }
    }
    printf("%lld\n", cnt);
    return 0;
}