#include<stdio.h>
bool prim[2000000];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    int N,i,j,nr=0;
    scanf("%d",&N);
    prim[1]=1;
    for(i=2;i<=N;i++)
        if(prim[i]==0) 
            {
                nr++;
                for(j=2*i;j<=N;j=j+i)
                prim[j]=1;
            }
    printf("%d",nr);
    return 0;
}