按题意直接模拟即可。

AC code：

#include <bits/stdc++.h>
using namespace std;
const long long MOD = 127237991;
long long mod_pow(long long base, long long exponent, long long modu) {
    long long result = 1;
    base %= modu;
    while (exponent > 0) {
        if (exponent % 2 == 1) {
            result = (result * base) % modu;
        }
        base = (base * base) % modu;
        exponent /= 2;
    }
    return result;
}

int main() {
    long long n;
    cin >> n;
    if (n == 0) {
        cout << 0 << endl;
        return 0;
    }
    long long result = mod_pow(2, n - 1, MOD);
    cout << result << endl;
    return 0;
}