codeforces round #234B(DIV2) B Inna and New Matrix of Candies

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <set>

using namespace std;

int main(){
    int n,m;
    cin >> n >> m;
    set<int> distance;
    bool flag = true;
    for(int  i = 0 ; i < n; ++ i){
        string rectangle;
        cin >>  rectangle;
        int dwarf_pos = rectangle.find(‘G‘);
        int candy_pos = rectangle.find(‘S‘);
        int dist = candy_pos - dwarf_pos;
        if(dist > 0) distance.insert(dist);
        else flag = false;
    }
    if(!flag) cout<<-1<<endl;
    else cout<<distance.size()<<endl;
    return 0;
}