#include <iostream>
#include <vector>
#include <string>
#include <math.h>
#include <cmath>
#include <algorithm>
using std ::cin;
using std ::cout;
using std ::string;
int perevod (char cc) {
    if (cc - '0' <= 9) {
       return cc - '0';
    } else {
        return cc - '0' - 7;
    }
}

bool podh (std ::string aa, std ::string bb, std ::string cc, int pp) {
    long long fir = 0;
    for (int ii = aa.size() - 1; ii >= 0; --ii) {
        fir += perevod(aa[ii]) * pow(pp, aa.size() - 1 - ii);
    }
    long long sec = 0;
    for (int ii = bb.size() - 1; ii >= 0; --ii) {
        sec += perevod(bb[ii]) * pow(pp, bb.size() - 1 - ii);
    }
    long long thrd = 0;
    for (int ii = cc.size() - 1; ii >= 0; --ii) {
        thrd += perevod(cc[ii]) * pow(pp, cc.size() - 1 - ii);
    }
    if (fir + sec == thrd) {
        return 1;
    } else {
        return 0;
    }
}

int main() {
    std ::string ss, aa = "", bb = "", cc = "";
    std ::cin >> ss;
    int minn = -1;
    int pos = 1;
    for (int ii = 0; ii < ss.size(); ++ii) {
        if (ss[ii] != '+' && ss[ii] != '=') {
            if (perevod(ss[ii]) > minn) {
                minn = perevod(ss[ii]);
            }
            if (pos == 1) {
                aa += ss[ii];
            } else if (pos == 2) {
                bb += ss[ii];
            } else {
                cc += ss[ii];
            }
        } else {
            ++pos;
        }
    }
    ++minn;
    for (int ii = minn; ii <= 36; ++ii) {
        if (podh(aa, bb, cc, ii)) {
            cout << ii;
            return 0;
        }
    }
    std ::cout << -1;
    return 0;
}