#include<bits/stdc++.h>
#define LINT long long int
#define ULINT unsigned long long int
#define INF 99999999999

using namespace std;

template<typename tmp>
void input(vector<tmp>& vc) {
    for (tmp& x : vc)
        cin >> x;
}
template<typename tmp>
void output(vector<tmp>& vc, string endll = " ", string endd = "\n") {
    for (tmp& x : vc)
        cout << x << endll;
    cout << endd;
}
int f(string s) {
    vector<pair<int, int> > vc;
    int c = 0, tmp, index = 1;
    for (int i = 0; i < s.size(); ++i) {
        if (s[i] == '{') {
            c++;
            vc.push_back({i + 1, 1});
        } else
            if (s[i] == '}') {
                c--;
                vc.push_back({i + 1, -1});
            } else
                if (s[i] == '=') {
                    tmp = i;
                    index++;
                    break;
                }
    }

    if (abs(c) > 1)
        return -1;
    if (c != 0) {
        if (c > 0) {
            int sum = 0;
            for (int i = vc.size() - 1; i >= 0; --i) {
                sum += vc[i].second;
                if (sum == c)
                    return vc[i].first;
            }
        } else {
            int sum = 0;
            for (auto& x : vc) {
                sum += x.second;
                if (sum == c)
                    return x.first;
            }
        }

    }
    vc.clear();
    c = 0;
    for (int i = tmp + 1; i < s.size(); ++i) {
        if (s[i] == '{') {
            c++;
            vc.push_back({i + 1, 1});
        } else
            if (s[i] == '}') {
                c--;
                vc.push_back({i + 1, -1});
            }
    }

    if (abs(c) > 1)
        return -1;
    if (c != 0) {
        if (c > 0) {
            int sum = 0;
            for (int i = vc.size() - 1; i >= 0; --i) {
                sum += vc[i].second;
                if (sum == c)
                    return vc[i].first;
            }
        } else {
            int sum = 0;
            for (auto& x : vc) {
                sum += x.second;
                if (sum == c)
                    return x.first;
            }
        }
    } else
    return -1;

}

int main(){
    string s;
    getline(cin, s);
    cout << f(s);
}