#include <stdio.h>
#include <string.h>

int main() {
    char s[1000];
    char ans[1000];
    char curStr[1000];
    scanf("%s", s);
    int n = strlen(s);
    int i = 0; int maxcnt = -1;
    int isLastDigit = 0;
    int curCnt = 0;
    for (i = 0; i < n; i++) {
        if (isLastDigit == 1) {
            if (s[i] >= '0' && s[i] <= '9') {
                curCnt++;
                curStr[curCnt - 1] = s[i];
            } else {
                if (maxcnt < curCnt) {
                    int j = 0;
                    maxcnt = curCnt;
                    for (j = 0; j < maxcnt; j++)
                    ans[j] = curStr[j];
                    ans[maxcnt] = '\0';
                }
                curCnt = 0;
                isLastDigit = 0;

            }
        } else {
            if (s[i] >= '0' && s[i] <= '9') {
                isLastDigit = 1;
                curCnt = 1;
                curStr[curCnt - 1] = s[i];
            }
        }
    }

    if (isLastDigit == 1) {
        if (maxcnt < curCnt) {
            int j = 0;
            maxcnt = curCnt;
            for (j = 0; j < maxcnt; j++)
                ans[j] = curStr[j];
            ans[maxcnt] = '\0';
        }

    }
    if (maxcnt == -1) printf("-1");
    else printf("%s", ans);

    return 0;
}