#include <cstdio>
bool d[1000000];
int c[999999];
int main() {
    int i,j,r=0,n;
	for(i=4;i<=999999;i+=2)d[i]=true;
    for(i=2;i*i<=999999;i++) {
        if(d[i])continue;
        for(j=i*2;j<=999999;j+=i)d[j]=true;
    }
	for(i=1;i<999999;i++) {
		c[i]=c[i-1];
		if(!d[i+1])c[i]++;
	}
    while(scanf("%d",&n)!=EOF) {
        printf("%d\n",c[n-1]);
    }
}