No of ways you can get a sum 'total' when n dice with m ways are thrown

#include <iostream>
#include <vector>
using namespace std;
vector<int> vec;//for counting total number of ways.
int sum(int m,int n,int total);//function prototype

int main()
{
    int n,m,total;
    cout<<"Enter the values of n,m,total respectively"<<endl;
    cin>>n>>m>>total;
    sum(m,n,total);
    cout<<vec.size()<<endl;
    return 0;
}
int sum(int m,int n,int total){

for(int i=1;i<=m;i++){
         if(n>=0&&total-i==0)
                 vec.push_back(0);//size of vector increases with each pushback,and no 
                                  //no of ways =vec.size()
                         
             if(n<0)
                    return 0;
               else
                     return  sum(m,n-1,total-i);

}

}