#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, count = 0;
  string s;
  cin >> n >> s;
  for (int i = 0; i < n; i++) {
    if (s[i] == '1') {
      count++;
    } else {
      if (s[i - 1] == '0')
        cout << '0';
      else
        cout << count;
      count = 0;
    }
  }
  cout << count;
  return 0;
}
