#include<stdio.h>
int n,x,y,c,z,v[2000002];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    x=2;
    z=0;
    while(x<=n)
    {
        if(v[x]==0)
        {
            z++;
            for(y=2*x;y<=n;y=y+x)
            {
                v[y]=1;
            }
        }
        x=x+1;
    }
    printf("%d",z);
    fclose(stdin);
    fclose(stdout);
    return 0;
}