#include <stdio.h>

int N, cnt;
char prim[2000005];

int main(void)
{
    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])
        {
           cnt++;
           for (j=i+i;j<=N;j+=i) prim[j]=0;
        }



    }


    printf("%d\n", cnt);

    return 0;
}