#include <cstdio>

char v[2000000];
int n,i,j,c;

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