阅读程序写结果：

#include <iostream> using namespace std; const int SIZE = 100; int main() { int p[SIZE]; int n, tot, i, cn; tot = 0; cin >> n; for ( i = 1; i <= n; i++ ) p[i] = 1; for ( i = 2; i <= n; i++ ) { if ( p[i] == 1 ) tot++; cn = i * 2; while ( cn <= n ) { p[cn] = 0; cn += i; } } cout << tot << endl; return(0); }

输入：30

输出：___