#include <iostream>
#include <string>
using namespace std;
int main()
{
    char s[30001];
    int a;
    cin >> a;
    for(int i=0; i<a; i++) cin >> s[i];
    int res=0;
    bool ok=false;
    while(!ok)
    {
             ok=true;
             for(int i=0; i<a-1; i++)
             {
                     if(s[i]=='>' && s[i+1]=='<')
                     {
                                  s[i]='<'; s[i+1]='>';
                                  res++;
                                  ok=false;
                                  i++;
                     }

             }
             //cout << s << ' ' << ok << endl;
    }
    cout << res << endl;
    return 0;
}

I used very similar code and got AC (though there is a better solution if I recall correctly). What I did is:
- Use stdio instead of iostream: it's faster
- If you have <<< at left end or >>> at right and, you can ignore those - they will never change again. Thus, you can keep treack of the left and right endings, and only parse those, instead of going from 0 to n every time.

AC 0.625