#include <stdio.h>
int N, c;
char prim[2000005];
int main()
{
    int i,j;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&N);
    for(i=2;i<=N;++i)
        prim[i]=1;
    for(i=2;i<=N;++i)
        if(prim[i])
        {
            ++c;
            for(j=i+i;j<=N;j+=i)
                prim[j]=0;
        }
        printf("%d",c);
    return 0;
}