Revise paste Untitled

#include <iostream>
#include <cmath>
using namespace std;

int main() {
    int n;
    cin >> n;
    string s;
    cin >> s;
    
    if(n <= 20) {
        int comb = 0;
        for(int mask = 0; mask < (1 << n); mask++) {
            string tmp = "";
            for(int i = 0; i < n; i++) {
                if(mask & (1 << i)) {
                    tmp += s[i];
                }
            }
            int number = 0;
            if(tmp.size() >= 3) {
                number = (100 * (tmp[tmp.size() - 3] - '0')) + (10 * (tmp[tmp.size() - 2] - '0') + tmp[tmp.size() - 1]);
            }
            else if(tmp.size() >= 2) {
                number = (10 * (tmp[tmp.size() - 2] - '0')) + (tmp[tmp.size() - 1] - '0');
            }
            else if(tmp.size() >= 1){
                number = (tmp[tmp.size() - 1] - '0');
            }
            if(number % 8 == 0) {
                comb++;
            }
        }
        int mod = 1e9 + 7;
        cout << (comb % mod) - 1 << endl;
    }
    return 0;
}