#include <cstdio>

using namespace std;

int n,i,j,nr;
char vaz[2000010];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++)
        if(!vaz[i])
        {
            nr++;
            for(j=i*i;j<=n;j+=i) vaz[j]=1;
        }
    printf("%d",nr);
    return 0;
}