#include <stdio.h>

int n, s;
char ciur[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)
        ciur[i]=1;
    for(i=2;i<=n;++i)
        if(ciur[i])
        {
            ++s;
            for(j=i+i;j<=n;j+=i)
                ciur[j]=0;
        }

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

    return 0;
}