#include <stdio.h>

int N, cnt,i,j;
char prim[2000005];

int main(){    
    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);
}