#include <iostream>
#include <cstdio>
using namespace std;
const int nmax = 2000005;
bool ciur[nmax];
int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int n, i, j, nr=1;
    scanf("%d", &n);
    for(i=3; i<=n; i+=2)
        if(!ciur[i])
        {
            nr++;
            for(j=i*i; j<=n; j+=(i<<1)) ciur[j]=1;
        }
    printf("%d\n", nr);
    fclose(stdin);
    fclose(stdout);
    return 0;
}